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Understanding Global Warming
Humanity will likely "survive" this century,
but in what state is up to us.
normal for local 'weather' to be hard to forecast, and change rapidly
(within a general range). But does the same apply to the holocene climate that threatens to heat up substantially faster than the prehistoric late paleocene?
Climatic "signal" vs. "noise" (fluctuation from ocean & solar cycles): Just the beginning (Updated here)
Not only do people wonder why
climate change is a problem when it "happened in the past" (see
below), but they question the existence of any evidence. Yet it has
been accessible for many years (examples here, here, and here).
We have a
rise in the decadal averages in three major surface datasets (affirmed
by the tropospheric satellite record), borehole analysis, global ocean
heat content (erroneous claims of cooling aside), widespread glacier disintegration,
rapid sea ice "rot"
(excepting Antarctica's special case),
thousands of bio-markers, increasing ratios of record high to record low
temperatures, a rising tropopause, increasing water vapor
as temperatures rise, thawing permafrost...
All combined with the well-established infrared
absorption properties of CO2/CH4, and a reduction of
infrared energy emitted from Earth. There's a distinct human fingerprint
in the climate of the last several decades, despite the
temporary offsetting effect of
things like sulfur pollution and natural variability.
moved beyond just strengthening the attribution case, to refining
projections based on physical processes (linear and otherwise),
paleoclimatology, and trends in human activity. Uncertainty
remains on a number of details, partly because there's no exact
prehistoric analog to our situation (a relatively rapid,
globally-distributed forcing coupled with a black carbon influence, and
mixed with the short-lived cooling effect of sulfates). But the main
conclusions are solid,
and the stakes are high for the most populous civilization to exist
on Earth. There is, though, a disconnect between the mainstream
community and the controversy-driven media. That would include claims
that global warming doesn't affect weather (when over time it can't help
but do so), and of it "stopping" every time there's a short down-tick
in surface temperature, vs. a statistically significant trend visible even on smaller timescales:
What the scientific community is saying (reflecting the consensus among actual published researchers):
credible body of scientific evidence shows that climate change is
occurring, is caused largely by human activities, and poses significant
risks for a broad range of human and natural systems...
- National Academy of Sciences The bottom line is that CO2 is absolutely, positively, and without
question, the single most important greenhouse gas in the atmosphere. It
acts very much like a control knob that determines the overall
strength of the Earth’s greenhouse effect... - Dr. Andrew Lacis, NASA climatologist To slow the rate of climate change, we can decrease the amount of carbon dioxide that we release into the atmosphere. - National Center for Atmospheric Research
There is no single threshold above which climate change is dangerous
and below which it is safe. There is a spectrum of impacts. But some of
the largest impacts are effectively irreversible and the thresholds for
them are very near... In particular, the melting and breakdown of polar ice sheets seems
to be in the vicinity of a couple of degrees warming. This expectation
is based on current high rates of mass loss from the ice sheets
compared to relative stability through the Holocene (the past 10,000
years) and on past ice sheet response in periods such as the Pliocene
(a few million years ago) when the Earth was a couple of degrees warmer
than preindustrial times (and sea level up to 25m higher)... - Dr. James Risbey, CSIRO Australia
Recent observations confirm that, given high rates of observed
emissions, the worst-case IPCC scenario trajectories (or even worse)
are being realized. For
many key parameters, the climate system is already moving beyond the
patterns of natural variability within which our society and economy
have developed and thrived. These parameters include global mean
surface temperature, sea-level rise, ocean and ice sheet dynamics,
ocean acidification, and extreme climatic events. There is a
significant risk that many of the trends will accelerate, leading to an
increasing risk of abrupt or irreversible climatic shifts. - 2009 Copenhagen climate congress of 2,500 scientists
The Earth's climate is now clearly out of balance and is warming. Many
components of the climate system—including the temperatures of the
atmosphere, land and ocean, the extent of sea ice and mountain glaciers,
the sea level, the distribution of precipitation, and the length of
seasons—are now changing at rates and in patterns that are not natural
and are best explained by the increased atmospheric abundances of
greenhouse gases and aerosols generated by human activity during the
20th century... - American Geophysical Union
There is no doubt that Greenland ice loss has not just increased above
past decades, but it has accelerated. The implication is
that sea level rise estimates will again need to be revised upward. - Dr. Jason Box, Glaciologist
It’s not the right question to
ask if this storm or that storm is due to global warming, or is it
natural variability. Nowadays, there’s always an element of both. - Dr. Kevin Trenberth, NCAR
As humans burn enormous amounts of fossil fuel (containing carbon removed over eons from the prehistoric atmosphere), gigatons of
carbon dioxide are accumulating beyond the uptake capacity of
today's natural "carbon sinks". With this imbalance, atmospheric concentration
has increased 39% since industrialization, rivaling the smaller and much
slower oscillations of glacial cycles, and reaching it's highest in at least 800,000 years. Other studies (Pagani et al., Pearson & Palmer, Hönisch et al.) suggest millions of years. And although there's some short-term fluctuation, the trend persists (accelerates).
This has changed the infrared transparency of Earth's atmosphere in
much the same way a drop of ink changes the visible transparency of
water. So what's wrong with this change, and how can we improve the odds
of ecosystem integrity and human prosperity into the future? First, a
crash course on the basics.
A small percentage of the atmosphere,
CO2 is nevertheless the primary persistent
"greenhouse gas", re-radiating heat energy over an atmospheric lifetime of several years. But a significant accumulation (total volume in the atmospheric column being what's important), exceeding the carbon cycle's quasi-equilibrium,
can last centuries and subside over millennia. After all, CO2 molecules aren't just absorbed
in nature, they're also re-released. Carbon is constantly exchanged between
the oceans, atmosphere, and biosphere, so seemingly modest atmospheric "residence times" are misleading. The net uptake resulting from a pressured carbon cycle would slowly
reduce the total "pool" once emissions fall (assuming no big feedbacks beforehand). But like an overflowing bathtub with a slow
drain, the input must drop below the sink rate. Then, even with no
biological sink reduction, carbon transfer rates to the deep ocean are an absorption
"bottleneck". So barring fantastical future advancements in carbon sequestration, today's buildup is a very long term commitment.
Carbon dioxide plays vital roles in climate and the biosphere, but
there can be too much of a good thing. A buildup amplifies the greenhouse effect that keeps Earth's average temperature above zero, causing warming (2).
Research overwhelmingly indicates this is the main factor in a climatically
strong trend, with much of the extra heat absorbed and
distributed by the oceans (their thermal inertia produces a lagged
atmospheric response). This rise, subject to fluctuation from things
like ocean cycles (in the exchange of heat between the depths and the
surface) and sulfate "aerosol", is extensive but not uniform, and proxy
studies suggest it has already exceeded anything in at least 2,000
Heat is the ultimate driver of the climate system.
Effects on evaporation, all forms of precipitation, reflective ice
and atmospheric circulation, and storm intensity make
change" a more complete descriptor of the situation. Although it's still
early in the process, and there are variables between climate
change and disaster losses that so far make direct attribution
between them difficult, trends in heat waves and precipitation are already
clear. And along with fast
responses like increasing levels of water vapor (a reactive greenhouse gas), protracted warming
is also subject to amplification by an interplay of longer-term feedbacks, like reduced carbon storage (example1, 2, and 3), and the release of more greenhouse gas from warming oceans, forests, peatlands, and tundras. Higher wildfire incidence and increased CO2 and methane emission from thawing permafrost
(See sidebar) are examples. How fast carbon cycle
effects will be is uncertain, but even the substantial mid-range climate
projections have insufficiently assessed their potential, and with
improved understanding of amplifying feedbacks and their lasting
dominance, concerns have only grown.
Warming may not seem like an urgent problem in most temperate regions, where so
far it has been largely subtle and mixed with significant variability. But it
does have the potential to cause lasting disruption, since many things
in today's world are vulnerable to rapid change. The rate
of warming is a key to how ecosystems and large human populations will
be impacted. Many a scientist would say past climate change has helped
shape humanity (usually in large-scale transitions over thousands or millions
of years), but so has the relatively mild, stable holocene in which
intensive agriculture and modern civilization have developed,
allowing us to expand our horizons beyond the mere struggle for
Nature is not
without resilience, but with cumulative pressures, biomes can weaken and change can snowball. Yet we can limit
it's progression and protect the biologically-rich interglacial that has
thrive. Markets are more globalized, so this
will take international efforts to reduce emissions from sources like
electric generation, animal agriculture, and transport (none of which
are likely to realize sufficient cuts alone).
As well as
technology to handle changes underway. And those in the middle and upper classes, who've benefited
most from a fossil-fueled system, are the ones more likely to have the
means to foster change.
Still, certain economic and ideological forces seek to cast
doubt on strong science, or downplay the negatives while emphasizing
some regional benefit (from moderate warming). An industry of disinformation has arisen, similar to past efforts to deny the health effects of cigarettes, with some of the same players (below). And those PR operations
have helped delay a stewardship-oriented approach.
Delay means locking in stronger impacts,
on agriculture and
resource reliability. This issue is about rapid climate change, and its many effects
on today's biosphere. If we stop ourselves from
pushing too far, we at least have the chance at several thousand years
of advancement; to become more resilient as a civilization, not just as a
1• "They can't even predict next week's weather"/"Models are useless"
As Dr. William Connolley notes, weather and climate aren't the same thing, and "predicting
one isn't the same as the other. Consider (analogy: not perfect but not
bad) the shore of the ocean and the level of the sea: tides can be
predicted with great accuracy years in advance; waves can't be
predicted any better than weather."
ultimately affected by warming, weather events are also influenced by
short-term ocean-atmosphere dynamics, and are more about the movement of heat and moisture within the system, while climate is more a function
of persistent, large-scale factors. It's convention to
use long-term averages as a basis for
detecting change, because weather "noise" tends to cancel out over
time, revealing the "signal" of a changing climate.
Computer models of highly variable local weather are actually more error-prone than those of climate trends. Although
some people demonize models in general (a key tool in
many aspects of science and medicine), the real consideration is how
scientifically robust they are. Modern
general circulation models are valuable for analyzing influences from
greenhouse gases to solar flux, and they produce large to medium scale
simulations that agree well with the real world. They're continuously
validated (Example), and refined with the latest data and cutting-edge physics. Yet their indicated trends have persisted, and no
model can account for them without including human-generated greenhouse
gases. GCMs have done a good job of projecting average temperature
change, the magnitude of short-term volcanic cooling, the
amplification of Arctic warming, an increase in heat waves and drought,
ocean warming, and the stratospheric cooling effect (#24).
Still, as in any science we can't expect perfection. Detailed
projection (particularly of complex regional climates) is difficult,
and probability analysis is important. But models needn't be exact to
give an indication of a trend and it's major effects. While there are
uncertainties, recent research suggests models may be inadequately
assessing amplifying feedback potentials. Something that would make at
least the longer term projections too conservative. Those who argue
against climate concerns by pointing to uncertainties in models tend to
ignore the possibility that they won't turn out in our favor.
take advantage of the public's weather-oriented perspective when
highlighting lower-end warming projections of "only" a few degrees. The
IPCC fourth assessment, representing reviewed and assessed
research, included a "best estimate" range of 1.8 - 4.0°C (3.24 -
7.2°F, Δ T) by 2100, with a potential range of 1.1 - 6.4°C
(1.98 - 11.52°F). This is based on several scenarios, with the low
end assuming a world with stabilized population and a quick transition from
fossil fuels, and the top numbers assuming high
emissions. Later studies based on continuing emissions growth indicate a rise of 4-7 degrees C. One of the
latest from Hadley Centre (here) suggests that on today's path, we could see 4 degrees
C as early as 2060. Top
climatologists view warming of about 2°C (3.6°F) this century
as a hazard point, beyond which broadly disruptive changes become much more likely.
Many studies suggest a "climate sensitivity"
of around 3°C (5.4°F) for a doubling of pre-industrial CO2
(something that could easily occur without mitigation). The AR4 notes that it's "likely to be in the range 2 to 4.5°C with a best estimate of
about 3°C, and is very unlikely to be less than 1.5°C. Values
substantially higher than 4.5°C cannot be excluded, but agreement of
models with observations is not as good for those values." More here. For local weather, a single-digit change over decades may not seem like much, but a global average
temperature increase of a few degrees is large, translating to
stronger regional effects, including from concentrations of extra
energy within the system. To help put things into perspective, the anomaly associated with early 20th century warmth was less than 1°F. The global mean temperature during the last glacial period was about 9°F lower than today's, and much of that seems to have occurred more slowly. Since then, things have been relatively stable, aiding the development of agrarian societies.
Dr. Ray Pierrehumbert notes: "So
far we haven't quite gotten to 400ppm CO2, but we'll eventually go to
700 or more without controls. We haven't even seen the full warming
effects of that 400ppm yet, because it takes time for the ocean to warm
up. So, the striking thing is that it has already gotten to the point
that the recent warming stands out from the natural variability of the
past thousand years or more, despite the fact that so far we've only
experienced the barest beginnings of the warming. That's not just
striking. It ought to be alarming."
Dr. Tim Flannery: "Our
deep psychological resistance to thinking that "warm" might be bad
allows us to be deceived about the nature of climate change. Those who
have exploited this human blind spot have left many people - even the
well-educated - confused. This is the result of an unhealthy, in some
instances corrupt, relationship between government and industry."
People often do see warmth as "nice", until winter
ends or the warmth is accompanied by drought, ecological impacts,
insect invasions, floods, changing croplands, more severe weather, or high wildfire danger.
3• "But the weather is downright chilly in ________/We hit a record low!"
warming refers to global average temperature change over time (an
indicator of Earth's "energy budget": Energy in vs. energy radiated to
space). It doesn't mean constant, regionally synchronous change or the end of cold snaps. Despite the
trend, fluctuations continue in a fluid-dynamic system, particularly from the variability in ocean heat exchange and heat distribution . These maps give some idea of how anomalies can vary on short timescales, especially regionally:
Vs. average anomaly for 2010 as a whole, and for the past decade:
will also occur more frequently with global warming (already observed, with
record highs occurring about twice as often as record
lows over the past decade), but local extremes alone are not
necessarily global indicators. It can be interesting, though, to
consider the circumstances under which records are set. Frequently
anomalous warmth despite the cooling influence of la niña,
increased Asian emissions of sulfur particulates, and a deep solar
minimum could be viewed differently from past warm spells under the
An example of a trend in record temperature ratios, expected to accelerate:
And when we look at the global averages, most of the warmest years are in the past decade:
Still, the weather we observe is an interplay of both natural variability (such as from
ocean cycles) and the cumulative human influence. And
perceptions can mislead. People don't think of global mean temperature
being on the rise when they're in the middle of a winter storm. Many
regions experience frosty spring weather, and lingering snowfall can
give a strong impression of cold even when temperatures aren't
unusually low. And under favorable conditions, water vapor feedback
from a warming planet can make regional snow & ice events more
intense, via the mixing of moister air.
4• "Climate change is normal/has happened throughout Earth's history..."/"CO2 levels have been higher before"
events do nothing to support the idea that today's ongoing process
is mostly natural, or irrelevant to Earth's present ecology. Although
there are generally-modest holocene fluctuations from things like
sulfates, solar cycles, and El Niño/La Niña oscillations,
warming from the carbon imbalance is on top of those. Significant global-scale changes
in the past have generally occurred over many millennia (instability
related to glacial period termination being an exception), allowing
life to adapt or
migrate. Warming from unabated emissions will likely be stronger, more
widespread and more persistent than anything seen by
civilization. Without this, Earth may well have thousands of years more of mostly stable, mild climate (see below).
As for CO2, there have been periods in pre-history with higher
concentrations, but climate and ecosystems
were starkly different (and again, a big issue today is the rate
of change). There were also periods when CO2 was relatively high but
temperatures weren't as warm as one would expect. That's because
of climate factors like solar irradiance, which was lower and has slowly risen over millions of years (some fascinating
If we could go back
in time and double Earth's CO2 concentrations (which we're poised to do
serious mitigation), that would have consequences. But not the exact
same consequences as racheting up CO2 levels in the middle of
5• "But most of the warming occurred before 1940"/"What about past events
like the medieval warm period?", and "Isn't Earth just recovering from
the 'Little Ice Age'?"
The first point is misleading and incorrect.
NASA notes that "More specifically, there was slow global warming, with
large fluctuations, over the century up to 1975 and subsequent rapid
warming of almost 0.2°C per decade." Despite some regionally
concentrated heat, events of the 1930's were much less significant
globally than the recent trend (example: 1930's vs. the 1990's & beyond), and were likely related to a period of moderately higher solar activity, with oceanic heat distribution helping determine local effects.
(so-named to attract colonists, when most of it wasn't green) hasn't
always been representative of major global trends, but change there had
been limited in scope during recorded history. And today's situation is
still progressing. Dr. Raymond Bradley of the UMASS Climate System
Research Center notes that "human activity is pushing warming at a much faster rate than in the past",
and NASA's Evelyne Yohe notes that the Arctic warmth of the early
1930's was the result of three decades of gradual warming. Even the
change of the past decade or so has exceeded that.
indicates that the "Medieval Warm Period" (and the moderate cooling
dubbed the "Little Ice Age") was comprised of non-synchronous regional
changes, and had relatively little impact on the global averages.
It also occurred over centuries (more detail on it here). The 2007 AR4 references proxy studies,
independent of the "hockey stick" (links bar), affirming that the
global magnitude of medieval warmth was weaker than that of today. Dr.
Michael Mann also addresses this here
(and for an example of a contrarian trick that makes it appear
otherwise, or that the current trend is part of a natural cycle, see
sidebar). The "mid-holocene warm period", about 6000 years ago, is a similar story, with high-latitude seasonal warmth.
It has even been suggested that the trend is part of a recovery from the "little ice age". Not only does evidence suggest it wasn't a globally synchronous event either, but a trend can't be called a recovery if natural mechanisms can't account for it (see below).
6• "The temperature record is too short to suggest human influence"
determination of anomalous global change, and the expectation that it
will worsen under "business as usual", doesn't depend solely on human temperature records. We also
have observations of radiation imbalance, studies on climate sensitivity, the physics of the greenhouse effect (infrared re-radiation), observed ocean warming that fits with
the amplified greenhouse effect, independent proxy datasets, and other
evidence for ongoing change in the averages, in the absence of an associated natural
7• "Isn't 'black carbon' from developing nations the problem?"
carbon (AKA soot) is viewed as a secondary contributor to climate
changes, with significant regional effects. The melting of some
glaciers may be attributed in
part to soot, from things like dirty coal-fired power plants, poorly regulated diesel engines, and developing nation stoves.
Soot is an easy target that would be relatively cheap to
address, and with more immediate effect, but research is ongoing as to
the likely net result of such targeted efforts. To some, this represents an
opportunity to shift attention from CO2 (even briefly), despite it being a much
larger long-term threat that will take more work to mitigate. It's
worth noting, though, that CO2 reduction and soot reduction can to some degree go hand-in-hand.
8• "What about claims of an impending ice age/ice age aversion?"
W. Felix, a former architect, received some publicity for his book and
website claiming that we're actually entering an ice age, and that
glaciers are growing (more below). These claims were repeated by
botanist David Bellamy, and posted on "skeptic" sites like Steve Milloy's "junkscience.com" (more). The assertions were traced to figures published by Fred Singer (who, like Milloy, was connected with TASSC, and also with dubious petition projects, below). Singer stated his source as "A paper published in 'Science' in 1989" - nowhere to be found.
It has also been suggested that we're averting another ice age by tipping the climate scale with greenhouse gas
emissions. Although we've probably already tipped that scale enough to
significantly delay a Milankovitch-type glaciation, indications are
that Earth is nowhere near due
for another glacial period anyway. Humanity has been blessed with one of
the longer interglacials. Still, there are those who have used
the ice age aversion argument as positive spin. They're essentially
implying that rapid holocene warming is fine because we'll avert the
multi-millennial cooling (or very rare, 'well-timed' supervolcanic
eruption) leading to the next big freeze. But if we're still around, we
can consider measured greenhouse gas emission/other geo-engineering to
avoid glaciation. For now, humans are in a period of development that may
eventually make us less vulnerable to disaster. It's in our interest to
value and prolong the time we have.
a related issue, there's a common myth that climatologists predicted an
imminent ice age in the 1970's, despite the infancy of the science
& technology, and acknowledged uncertainty on the future trajectory
of climate forcings. While there was some speculation (along with
caveats) and some overzealous media coverage, there's more to the story than today's naysayers admit. Update: A more recent review paper affirms what the scientific literature was actually saying.
9• "Natural processes will fix the imbalance"
is essentially true, but it leaves out two important factors: The
timescales involved and the damage done in the meantime. Once the
source diminishes, an imbalance tends to self-correct, but not
necessarily in a quick and convenient manner. During the
paleocene-eocene thermal maximum, carbon accumulation occurred over
10,000 years, and recovery took about 100,000. At this point, things
are a bit different, but not in a way that allows us to continue as
usual. In fact, evidence suggests humans are releasing carbon at a much higher rate
than the natural emissions leading into the PETM (which appears to have occurred with less than a doubling of carbon), and that climate
change in today's less warm-adjusted world has the potential to occur
faster. If this compromises Earth's carbon sinks, a
multi-millennial recovery wouldn't
be out of the question.
10• "Won't life just adapt?"
Rapid warming is a multi-faceted problem, with ecosystem impacts being
one result. Some organisms may readily adapt (many of them at the
expense of their populations), while others can't simply adjust in a
matter of decades or centuries. Thousands of species, including some
that play vital roles in complex ecosystems, are at risk (see link
section). More discussion here.
11• "What about religious views of global warming?"
those with a Bible-based perspective, the question becomes whether
there's direct divine control over Earth's life-supporting systems
(thus we can freely trash them), or whether a sustained
quasi-equilibrium has been set up that allows our
actions (born out of free will) to demonstrate either stewardship or
disregard. And which seems more responsible: To assume the former
because it's easy and convenient, or the latter because it's not worth
gambling with the future (a future that could be millennia, despite
ever-present predictions of apocalypse)? Several religious groups have
decided it's better to err on the side of caution and accept some
responsibility for the environment that sustains us. Others selectively
interpret the Bible as supporting careless plunder, while disregarding
passages that suggest such things as humanity's
12• "More solar activity is responsible, and Mars/Pluto prove it.
Some highlight the sun as the primary cause of global warming (often selectively citing snippets from Solanki et al. 2004),
the science doesn't support this. Although the sun goes through 11-year
activity cycles, and contributed to moderate (but regionally
significant) warming in the early 20th
century, it doesn't account for the strong 'trend' of recent decades. A
2006 NCAR study (Foukal et al.) affirmed with satellite and proxy data
that solar flux has made a negligible contribution to accelerated
warming over at least the past 30 years, and that luminosity changes
had a moderate influence over the past thousand years or more. Lockwood
& Frolich note in another study that "over the past 20 years,
all the trends in the Sun that could have had an influence on the
Earth's climate have been in the opposite direction to that required to
explain the observed rise in global mean temperatures". Other solar-related claims have also taken it on the chin. Additionally,
the stratosphere has been cooling (#24), consistent with an amplified
greenhouse effect but not with a significant increase in average solar output.
The latest standing scientific papers agree that the sun isn't driving the ongoing trend (more here).
trend that remained robust despite a deeper than average solar
minimum, the temporarily offsetting effect of natural and manmade
sulfates, and at least two ocean heat exchange cycles being in their
cool phases. In any case, elevated levels of greenhouse gas trap additional solar
energy whatever it's intensity. The fact that the greenhouse effect
strongly influences Earth's climate makes it an important part of the
equation. If it were allowed to snowball, and a period of
substantial solar warming were to occur in the future, one has to wonder
about the results. Re: Mars and other planets - Even if there were a global warming trend on Mars (vs. a changed polar ice cap over a few Martian seasons),
there are no oceans there, much of the ice isn't composed of water, and
the atmosphere is much thinner. So
temperatures are bound to be more sensitive to even small solar changes.
But as noted by
astrophysicist Steinn Sigurdsson, there are other factors at work on
Mars unrelated to the sun's output (which, overall, had been declining
slightly as it moved towards solar minimum). The much greater influence
of orbital eccentricity, strong seasonal variation, and the strength
& duration of hemispheric dust storms are also involved. And of
course that's a change on
of Mars over several years, vs. a trend over decades on Earth. For
Pluto, warming has been inferred from a change in atmospheric thickness
over less than one Plutonian season, following a close approach to the
sun. Other bodies in the solar system also have very long seasons and
orbital periods (even centuries), or surface conditions
driven mostly by internal energy sources, so they can't be used as solar
indicators either. More here on the climates of other planets.
13• "The CO2 increase is natural"/"Ocean warming is responsible for the rise in CO2."
question is, what's causing that ocean warming if solar activity can't
account for most of it? A few "skeptics" have suggested undersea
volcanoes, but a major activity increase (for which there's no
evidence) would be required to globally heat the oceans a fraction of a
degree, and they're also warming from the surface down. Earth's average geothermal heat flow
is negligible compared to the energy received from the sun or retained
by the greenhouse effect. A recent Scripps study (see sidebar) affirms
that patterns of oceanic warming are consistent with CO2 forcing (as are other changes). And in terms of CO2
exchange, the oceans still represent an absorption of about 2 GtC
(subject to decline as temperatures rise and
ocean chemistry changes). Even fossil fuel accounting, and the fact that
part of our carbon output doesn't remain in the atmosphere, indicates
that nature remains (at least for now), a net carbon sink, not a source. Scientists can also measure how much
CO2 is from fossil fuels:
14• "But ice core data shows that warming boosts CO2, not vice versa."
claim not only ignores the traceable origins of the current
accumulation (above), but it leaves out some important details.
During glacial period terminations, recovery of atmospheric CO2 acted as a
feedback to amplify warming triggered by Milankovitch orbital forcing.
This doesn't mean CO2 can't itself be a significant climate forcing (a cause of change rather than just a response). It just never has (until now) over the entire 800,000 year ice core record. More from Realclimate.
Jeff Severinghaus, Professor of Geosciences at Scripps notes: "All that the lag shows is that CO²
did not cause the first 800 years of warming, out of the 5000 year
trend. The other 4200 years of warming could in fact have been caused
by CO², as far as we can tell from this ice core data".
According to Caillon et al, 2003, "the CO² increase clearly precedes the Northern Hemisphere deglaciation"...
And referring again to our 650 kiloyear CO2 chart, we can see the other difference between then and now:
15• "Aren't the oceans actually cooling?"
study by Lyman et al showed a decrease in oceanic heat content from
2003-2005. Such variability wouldn't necessarily indicate a new trend. But there also seems to be an inconsistency in
this study: Sea level should have dropped along with temperature,
unless there's been a sharp increase in compensating ice melt. Ocean circulation
changes and variability in heat exchange with the deeper ocean are variability factors. While
the study is still under review, short-term inconsistency in warming
wouldn't be surprising. Update:
Peer review at work. Lyman study seems to have a data problem, cooling
has disappeared in latest analysis. And some discussion here and here of trends and updates since.
16• "What about methane?"
Although it's emissions and concentrations are much lower than those of CO2, methane is a
more powerful greenhouse gas, and has the potential to play a
significant role in future warming. Along with the again rising levels of directly human-induced emission, feedbacks are
likely to release more methane as warming progresses. One scenario,
modeled by an NCAR supercomputer, involves warmer water releasing
methane currently frozen under the sea floor (see sidebar). Thawing
permafrost, though, may have more feedback potential over the next
17• "Volcanic/other natural emissions far exceed those of humans."
Another volcanic gas, sulfur dioxide (SO²), can have a temporary cooling effect.
But the real issue is a significant change in CO2 concentration. Overall, natural CO²
emissions have been balanced by absorption. A simplified example: The
trees that burn in a forest fire contain carbon that was previously
removed from the atmosphere. As the forest regenerates, CO²
is re-absorbed. With continued warming, though, wildfires are expected
to become more frequent and severe, further disrupting the carbon
cycle. Update:Rise in wildfires linked to climate change.
18• "CO2 trend data from Mauna Loa is biased by the volcano"
are taken upwind from volcanic vents, out-gassing is monitored, and any
short-term spikes are flagged for removal, but even if the Mauna Loa
figures were tainted, the volcano can't explain a long-term upward
trend. There are also multiple isolated measurements around the
world, including in Antarctica, that agree well. More here on the choice of Mauna Loa, and here on measurement reliability/verification.
19• "Is deforestation affecting climate?"
fossil fuel combustion is the primary factor, deforestation results in
the release of about 1.6 gigatons of carbon annually. The impact is
highest in the tropics, in part because those forests (which tend to be
ecologically sensitive) are often burned for pasture, and changes are
often permanent or very long-term. Forest loss can reduce the
land-based carbon sink, and re-forestation can help offset carbon cycle
impacts, but net absorption rates are influenced by multiple factors,
including forest type and regional climate. Although tropical forests are often called the "lungs of the Earth" (and they are large carbon reservoirs), they are in fact less of a sink than the world's oceans.
20• "Extra CO2 will be beneficial/Plant growth will correct the imbalance."
It has been argued by certain fossil fuel interests that higher
CO² levels will enhance plant growth and benefit agriculture. This
is true to a point, under the right conditions. But in the real world,
plant growth and productivity are more limited by factors other than
CO2 concentration (which is already quite sufficient to support healthy
growth rates). Growing conditions are likely to change (insect populations, water availability, extreme weather events...), and a comprehensive Stanford University study
found that elevated CO² only stimulated growth when nitrogen,
water and temperature were at normal levels. It was also suggested that
excess soil carbon or initially accelerated growth may limit the
availability of nutrients. Some "weedy" plants may benefit
disproportionately from extra CO2, but they would need to somehow
overcome present-day geographic limitations and more than triple the
net terrestrial carbon sink to counter most of our current emissions. Any enhancement of a sink helps, but the accumulation already in progress is exceeding sequestration by plants, and oceanic dissolution. For more detail on considerations in agriculture, see the consequences page.
21• "What about the role of clouds and precipitation?"
contrarians have suggested that extra cloud cover might offset warming.
John Christy of UAH speculated on this, and also stated (to digress for
a moment) that "Whatever happens, we'll adapt". The question is how many
of Earth's billions of people (ecology aside) might adapt, at what
cost, and with what quality of life? Regarding clouds, though: Although
storm intensity may increase, rising temperatures also mean more water
can remain uncondensed in the troposphere. The likelihood of
significant cooling from thick, low-level cloud cover appears questionable. Additionally,
proponents of the cloud-cooling theory don't seem to indicate why
negative feedback had trouble keeping up with the last carbon
accumulation event in prehistory, or even how Earth has come out of
glacial periods despite a supposedly strong negative feedback. Betting
on altered cloud cover is
Depending on their type, clouds can reflect more energy than they trap
in the atmosphere or vice-versa. They can reduce daytime warmth, but
also keep overnight temperatures higher and provide a head-start for
daytime heating. An overall increase in winter lower-level cloud cover
and a reduction in the summer averages would have a warming influence.
The net effect is an area of intensive study. All
climate models project significant warming, but cloud behavior may help
determine whether it will be closer to the high end or the low end of
the range. Update: New research suggests the higher end. Spencer & Christy,
previously known for promoting a flawed satellite temperature
record, released a paper suggesting that an inter-annual
cooling effect in the tropics may have implications for the projection
of global warming. See How to cook a graph in three easy lessons.
22• "What about 'aerosols', contrails, and 'global dimming'?"
dimming refers to a reduction of solar energy at Earth's surface caused
by particulate/"aerosol" pollution and it's interaction with clouds.
Aircraft contrails also have a small (on average) effect, but this ends
up as a slight warming from infrared re-radiation. The cooling effect
of aerosols has partially masked global warming and presents what seems like a pollution control conundrum.
In the 1990's, this effect showed signs of declining, meaning
additional energy for the human-amplified greenhouse effect to trap.
This would make CO2 emission reduction that much more important.
Currently, particulates and sulfur dioxide (source of sulfate aerosol)
are reduced for the sake of cleaner air. CO2 output often goes
Another effect of these pollutants seems to be the
intensification of winter storms in the northern Pacific (and
disruption of vital Asian monsoons), and their circulation of warmer
air to the Arctic (Zhang et al, 2007). In other words, such pollution
may worsen warming-induced changes in some regions.
23• "Don't El Niño and La niña influence climate?"
are an oscillation related to the circulation of tropical Pacific heat.
The global average temperature impact of a strong El Niño is
about 0.2 degrees C. Although a significant natural
influence on weather patterns and contributor to inter-annual
fluctuation (see graph at the top of this page), the temperature
effects of the natural cycle smooth out over years, and aren't a cause of the
However, the effects of El Niño may be "enhanced" by global
warming, since the oscillation essentially pools oceanic heat and
alters moisture flow. Recent NASA and NOAA research suggests that much of the
increase in Pacific sea surface temperatures in recent decades has so far
manifested itself in the form of stronger, more frequent central
Pacific El Niños. Discussions of how the average magnitude and persistence of El Nino may be affected here and here.
24• "What about ozone, stratospheric cooling, and CO2 band saturation?"
sometimes confused in the media, stratospheric ozone depletion and
global warming are largely separate concerns. The main problem with
ozone depletion is higher levels of damaging ultraviolet radiation.
This is already being successfully tackled (see here
for more, including footnotes) with an international phase-out of CFCs
(ChloroFluoroCarbons), while global warming needs to be addressed via
reduced emission of greenhouse gases ("GHGs") like carbon dioxide. The
two issues, though, are somewhat interconnected.
CFCs (and some of their substitutes) and tropospheric ozone are also greenhouse gases (relatively minor
ones compared to CO2). And, as counter-intuitive as it may seem, the
amplified greenhouse effect causes stratospheric cooling (simplifying,
more GHG in the troposphere reduces infrared re-radiation to the
stratosphere). Ozone depletion itself contributes modestly to such cooling.
The claim that band saturation severely limits CO2 as a climate forcing is a myth (more here and here, and this on the claims of Ferenc Miscolczi),
derived from a concept widely considered flawed since the 1950's. The
upper atmosphere and the "wings" of the CO2 absorption band are rather
important, and models already represent CO2 forcing as the natural
log of it's change in concentration (leaving plenty of climate-shifting potential).
are popular half-truths, meant to mislead. Partly due to heat uptake by
the southern ocean and lower surface melt, ice sheets in East
Antarctica have remained relatively stable (consistent with model
projections), and appear to have received some extra snowfall. Some
thickening has also been observed in Greenland at high
elevations. This is related to the regional precipitation of extra
moisture, and is not inconsistent with a warming world. Despite this,
and a slight cooling in parts of Antarctica, most of the world's glaciers have been receding as part of an inter-decadal trend, and ice loss has accelerated in Greenland (resulting in a large net mass reduction).
Above is one example of feedback: A moulin (vertical shaft) carries meltwater to the
ice sheet base, where it can (depending on sub-glacial characteristics)
act as a movement-accelerating lubricant.
26• "Is there a link between warming and hurricanes?"
connection between recent hurricane strength and early-stage global
warming has been an area of some debate. The link with hurricane frequency is even more so.
It's typically not possible to prove a direct causal link with a
particular event, since such events are a confluence of regional
dynamics and the overall trends related to Earth's energy balance. Ocean
warming simply makes more energy and moisture available for potential
concentration, thereby increasing the odds of a severe
event. Research (such as Emanuel,
Knutson, Webster, Holland et al.) indicates an intensity trend
influenced by warming.As warmer temperatures spread north, tropical cyclones can also stay intact longer.
Even a seemingly small rise in sea
surface temperature means extra water vapor and energy for a storm to
pick up (while el niño or Saharan air layer conditions can periodically suppress hurricanes in the Atlantic). Then there is the element of rising sea levels
and their contribution to storm surge. Although the IPCC estimates are
often cited, those carried substantial caveats regarding dynamic ice
sheet disintegration, and the lack of thoroughly reviewed projections
for it as of the AR4. More recent research suggests we could see a foot
of sea level rise (on average) by 2050 and 4-6 feet by 2100. And some of
the newest, preliminary
research is exploring the possibility that high pressure blocking ridges
in a warming Arctic can influence the path of a storm like Sandy, so it's less likely to drift out to open sea.
meteorologists and media outlets have quickly dismissed any climate change connection,
ignoring the ongoing scientific inquiry, often focusing on frequency
rather than intensity, and chalking everything up to a natural Atlantic
cycle (controversy followed). The research, though, found an intensity trend in Pacific and Indian ocean storms as well. This earlier article addresses the issue further.
27• "Is there some level of consensus among climatologists?"
consensus isn't the point of science, and some might mock it, there have
been relatively few cases of established scientific tenets being
fundamentally overturned in modern Earth science. For
every Galileo-type challenge that succeeds in establishing an
alternative theory, there are many others that fail. In climatology,
the peer-reviewed literature and periodic assessments, and major
scientific organizations indicate wide agreement on several main
points, including that there's a significant human influence on climate:
28• "Climatologists exaggerate/perpetuate the concept of human influence for funding."
Ray Pierrehumbert put it: "Money and perks! Hahahaha. How in the world
did I miss out on those when I was a lead author for the Third
Assessment report? Working on IPCC is a major drain on ones' time, and
probably detracts from getting out papers that would help to get grants
(not that we make money off of grants either, since those of us at
national labs and universities are not paid salary out of grants for
the most part). We do it because it's work that has to be done. It's
grueling and demanding, and not that much fun, and I can assure
everybody that there is no remuneration involved..." And "...scientists
are probing theories and conceptions all the time, trying to break
them. The best way to become famous is to overturn established wisdom,
so scientists look hard all the time for opportunities to do this."
Further, much attention is applied to areas of uncertainty - something
climatologists concerned mainly about money would over-emphasize,
rather than affirming the primary role of human activity. We also have
the reality that many climate researchers are tenured/conduct research
as they see fit, and that funding goes into cutting edge research and
expensive equipment. Can the same be said of funds disbursed to
contrarians by the fossil fuel industry? Even the finding of a significant natural factor would attract research grants. And there have been decades of opportunity
for any number of skeptical scientists to overturn the case for anthropogenic influence. Instead it has grown stronger.
29• "So what can be done?"
change and our energy situation are big problems that require a
combination of solutions across multiple sectors. We need to start now
rather than simply betting on
technologies that may not be viable in time to avoid locking in
dangerous effects. Dr. Romm lays out one reasonable plan here, while discussing the "breakthrough technology illusion" here. Alternative
energy sources that result in little or
no net CO2 emission (from production or consumption) will play a role,
but there must be a focus on reducing waste/improving fuel efficiency
as well. The best way to spur such changes, and recognize the
externalized costs of fossil fuels, may be through a cap & trade
system that reduces their persistent cost advantage, and
provides rebates or incentives to consumers. Similar systems have been
supported in the past by even Republican administrations to phase lead
out of gasoline and moderate sulfur emissions (see sidebar). If that
isn't doable on the scale necessary to cut carbon output, we at least
need a concerted effort to redirect fossil fuel subsidies (direct and
indirect) to efficiency and alternative energy. In any case, the longer
society waits to quicken the transition, the more difficult and
expensive the future is likely to be.
For some basic things we can do now to address the issue of global climate change, see sidebar.
30• "Is 'clean coal' an option?"
coal technologies have the potential to reduce CO2 emission, but
significant cuts will only be made by gasification plants that
implement carbon capture and storage/sequestration (CCS). IGCC plants can make separation
economical, but the CO2 must then be compressed, transported, and
sequestered. Except where it can be sold for enhancing oil extraction,
this represents an expense unlikely to be widely accepted without ongoing subsidy and/or CO2 regulation. This and other problems with the technology (here) make large scale deployment unlikely in the foreseeable future.
As of this writing, there are no commercial CCS operations planned, but
this doesn't stop coal interests from advertising the technology as if
it were right around the corner. Additionally, "coal to liquid"
fuels represent a double CO2 pollution load unless CCS is employed.
Even then, there would be no difference between the impact of
coal fuels and petroleum fuels.
31• "Improving efficiency and cutting emissions will ruin our economy."
political organizations have released reports on the costs of acting
that provide little detail and ignore or underestimate the benefits.
Further delay is more likely to ruin our economy, both in terms of the
lasting effects of climate change, and rising fuel prices as demand
outpaces cheap extraction. Higher prices may be good for oil companies
with the most robust reserves, but they will impact everything produced
and/or transported with oil, including plastics, building materials,
and even food (think agricultural chemicals and diesel). The costs of
climate change alone are likely to be very steep compared to the costs
of acting to limit global warming. Economic implications and claims of
economic ruin are further discussed here (including the relevant link at the end) and here.
32• "But doesn't mean consumption/'cow emission' have more impact than fossil fuels?"
might seem like an odd one, but a 2006 UN report suggested that
livestock production results in (modestly) more greenhouse gas
emission, in CO2 equivalent, than the transportation sector. The 18%
figure includes methane (6%) and nitrous oxide (3%) output, and also
CO2 from forest burning & fossil fuel inputs (9%). Nitrous oxide
forcing has been growing moderately (recently 0.16 W/m2 vs. 1.66 for CO2)
and methane is so far lingering around 0.5 W/m2.
Another study suggested that up to 51% of human greenhouse gas forcing
can be attributed, directly or indirectly, to animal agriculture, but
controversy abounds given the difficulty of what they authors attempted
to do: Count respiration emissions that are typically considered
carbon-neutral. The jury is still out on the robustness of the numbers,
but suffice it to say that modern cattle production is a significant
contributor, and moderating meat consumption could be a larger part of
mitigating accelerated climate change. Meanwhile, though, CO2 emission
from transit and power generation continues to grow rapidly, and may
take more time to mitigate (since associated supply systems are
decade-scale investments). Therefore, it's important to address all significant sources, agricultural and otherwise.
the improvements of past decades spurred by clean air regulation, most
manufacturers have resisted applying efficiency technologies in a
significant way. But more automakers have released limited lines of
enhanced vehicles, and then developed advertising campaigns appealing
to concerns about fuel prices (concerns heightened by heavier,
inefficient personal vehicles). Recent increases in fuel economy
standards should finally spur some real change, and may eventually
produce a modest emissions reduction vs. continued emissions growth.
Vehicles that burn ethanol have also been touted, but
availability remains an issue in many regions and without further
efficiency improvements (in both production and combustion) the net
benefit is very limited. As production methods advance and agricultural
wastes are utilized, ethanol could be a valuable fuel, since the plants
used to produce it are part of the present-day carbon cycle (they
absorb atmospheric CO2 in order to produce the carbohydrates the fuel
is derived from). But the liquid transportation fuels with the most
promise for having a small carbon footprint (cellulosic ethanol,
biobutanol, and algal biodiesel) are not currently scalable or
commercially viable, and at present consumption levels they may have a
hard time gaining a foothold. This makes conservation more important
also been a lot of hype over hydrogen as a fuel. Although it may
some potential as the energy situation improves, widespread use would
likely be decades away at best. The key issues are the lack of necessary
infrastructure, the low energy
density of hydrogen compared with hydrocarbons, and the fact that
hydrogen isn't an energy source. It must be generated from
water or fossil fuels, and takes more energy to produce, store, and
distribute than it yields in combustion. Fuel cells may eventually
offer enough output and overall efficiency at reasonable cost, but
probably not anytime soon. Hydrogen hype may be beneficial to
oil & gas companies likely to be building infrastructure and
providing potential fossil feedstocks, and it may leave the impression
that they're making an effort to ease our petro-addiction. In reality,
focusing mostly on hydrogen will delay the transition from fossil
fuels, and require additional energy supply and higher efficiency to
34• "What about China?"
a common argument, often used to deflect responsibility, that China is
surpassing the U.S. in CO2 emission, but isn't required to improve
(therefore, the U.S. shouldn't bother). First, China did participate to
some degree in the early phase of Kyoto, but as a developing nation it
wasn't expected to return to 1990 emission levels. Second, America has
been emitting large amounts of CO2 longer, and still easily outpaces China in per-capita
emission. There are over a billion people in
China, yet their total output is nearly the same as ours. Some argue
that efficiency (at least industrial efficiency) is higher in the
U.S./CO2 emission is lower per unit of GDP. Differences in purchasing
power can influence that picture, and the U.S. has also shifted much of
it's energy intensive manufacturing overseas and become more of a "service
economy". As a result, we're indirectly responsible for part of China's
carbon footprint. Most countries can do better, but the U.S. is in a
position to help foster technologies globally.
35• "Hasn't the climate been cooling for years?"
This is an oldie that began with people like Pat Michaels (#2 above) and Geologist & prolific contrarian Bob Carter (here, here, and here). This claim takes advantage of annual to decadal fluctuation in atmospheric temperatures,
and is made by selecting a short, exceptionally warm period as a basis
for comparison. For example, the strongest el niño of the
century helped make 1998 a record year in the CRU surface dataset, with
2005 being a close second (the NASA and NOAA data, which unlike CRU represents
the fast-warming Arctic, pegs 2005 and 2010 as the warmest years on record). So
choosing 1998 as a starting point is a classic cherry pick.
Since climate change is based
on trends of greater than a decade, relative to a long-term
average, it's invalid to make claims based on individual years.
with later years (particularly those affected by la niña) being
a bit cooler, the averages remain anomalous in the longer-term context, and 11 of the warmest on record were in the last 13 years. And because the exchange of heat between the oceans and the atmosphere can vary, some modest near-term cooling of the atmosphere doesn't necessarily mean Earth is actually losing more heat. See here for more.
Flawed petitions used in attempts to debunk anthropogenic global warming
With petitions like these, some pertinent questions are: What does the
petition actually say, how was it presented, how many signatories were really scientists, and active in research climatology (vs. something like regional meteorology or petroleum geology)?
would be fools to risk so much to delay a transition that may initially
be a challenge, but also offers a myriad of environmental, economic,
and national security benefits. - Andy C Newburg
1. Adaptation responds to current losses.
2. Mitigation responds to future losses.
3. Adaptation plus future costs is more expensive than mitigation.
4. Adaptation without mitigation drives procrastination penalties to infinity. - J. Willard Rabett