Climate change denier and U.S. Senator James Inhofe (R-Okla) published a report just before Christmas with the headline: "Over 400 Prominent Scientists Disputed Man-Made Global Warming Claims in 2007." Does that leave you surprised and wondering? It shouldn't. It's a shocker of a headline, but the report itself doesn't back up the claim.

The Inhofe report is 156 pages long. The eight-page introduction – all that most people will read – describes the report and its goals, and gives selected highlights. The body of the report is a series of profiles starting with a sentence or two of biography followed by quotes questioning the validity of climate science.

The aim of the report is to refute that only a handful of scientists – mostly in the pocket of oil companies – still dispute that global warming is happening, and that it's caused by human activities. To this end, Inhofe's aides scoured the internet for quotes from skeptical "scientists".

I put this word in quotes because not all the "over 400 prominent scientists" are truly scientists. As the report itself states, the list includes economists and engineers. These may be smart people, but a smart person without expertise in climate science is still a person without expertise in climate science.

Some of these "over 400 scientists" have not published any climate science-related research. I did a search on the terms "climate," "weather," and "carbon dioxide" in the extensive ISI Web of Science database, and did not find, for example, James Hammond, a chemist; statistician Bjorn Lomborg (author of The Skeptical Environmentalist, not a peer-reviewed scientific publication); and physicist Antonio Zichichi.

Others are published, but while their results are consistent with the consensus view, their interpretations are not. For example, Duncan Wingham observed that the Antarctic ice sheet is growing rather than shrinking (true), but then said this is not "favorable to the notion we are seeing the results of global warming."

In fact, although the Greenland Ice Sheet is projected to melt and contribute to sea-level rise over the next century, the Antarctic is projected to gain ice in the near term due to heavier snowfall induced by global warming. The IPCC Fourth Assessment Report states:

Current global model studies project that the Antarctic Ice Sheet will remain too cold for widespread surface melting and is expected to gain in mass due to increased snowfall.

Then there are the many others making statements that are simply incorrect. The highlights of the report – presumably its best shots – contain one factual error after another. Here is a sampling, with responses from Michael Oppenheimer, a climate scientist at Princeton University and science advisor to Environmental Defense:

Even if the concentration of 'greenhouse gases' double man would not perceive the temperature impact. –Oleg Sorochtin

MO: Wrong. Earth is well short of a doubling of CO₂, yet changes are apparent not only to scientists, but to the "man in the street" – warmer winters, a melting Arctic. These are closely tied to the buildup of greenhouse gases.

The effect of solar winds on cosmic radiation has just recently been established and, furthermore, there seems to be a good correlation between cloudiness and variations in the intensity of cosmic radiation. Here we have a mechanism which is a far better explanation to variations in global climate than the attempts by IPCC to blame it all on anthropogenic input of greenhouse gases. –Boris Winterhalter

MO: This theory is decades old and has been examined closely. The underlying correlations have been shown to be spurious, and there is no physical mechanism shown to connect cosmic rays to climate.

To my dismay, IPCC authors ignored all my comments and suggestions for major changes in the FOD (First Order Draft) and sent me the SOD (Second Order Draft) with essentially the same text as the FOD. None of the authors of the chapter bothered to directly communicate with me (or with other expert reviewers with whom I communicate on a regular basis) on many issues that were raised in my review. This is not an acceptable scientific review process. –Madhav Khandekar

MO: All comments are reviewed closely – an independent review editor stands guard to assure this is the case – and almost all comments are taken into account. Incorrect comments are not incorporated into the text, and shouldn’t be.

We appear to be overplaying this global warming issue as global warming is nothing new. It has happened in the past, not once but several times, giving rise to glacial-interglacial cycles." –B.P. Radhakrishna

MO: Yes, warming has happened, but this is the first driven by humans, and it threatens to cause global changes within decades on a scope of natural changes that occur within millions of years.

We thus find ourselves in the situation that the entire theory of man-made global warming—with its repercussions in science, and its important consequences for politics and the global economy—is based on ice core studies that provided a false picture of the atmospheric CO2 levels. –Zbigniew Jaworowski

MO: Ice core studies are highly reliable, but are far from the only evidence. Computer simulations of the past are consistent with the models, and current changes in climate support the conclusions from both.

CO₂ is not the big bogeyman of climate change and global warming. Not CO₂, but water vapor is the most important greenhouse gas. It is responsible for at least 75% of the greenhouse effect. This is a simple scientific fact, but Al Gore's movie has hyped CO₂ so much that nobody seems to take note of it. –Luc Debontridder

MO: Water vapor is indeed an important greenhouse gas. And one of the key things about the CO₂-related warming is that it causes more water to evaporate from the ocean, amplifying the initial man-made warming.

Sadly, these errors may not be accidental. Many of the scientists on the list – and Senator Inhofe, himself – are associated with institutions funded by Exxon. These include the usual suspects – the Richard Lindzens and Fred Singers – that get quoted over and over again. For a list of names and connections, see this map. Gristmill also is looking into the background of the "Inhofe 400" in its "Skeptic of the Day" posts (here, here, and here).

As for the complaint that the IPCC and other scientific fora don't give a loud enough voice to the skeptical view point, we suggest that the proper channel for skeptics to voice their scientific concerns is through peer-reviewed publications and sanctioned assessments such as the IPCC and National Academy of Sciences reports. If their views are not fully reflected in those channels, it's because they don't stand up to rigorous scientific review.

The award of the 2007 Nobel Peace Prize to Al Gore and the Intergovernmental Panel on Climate Change (IPCC) is an important milestone in the journey toward a global warming solution, and it got me thinking about how the IPCC came to be. To some extent, it was thanks to a miscalculation by the Reagan Administration!

In the mid 1980s, I was head of the atmosphere program at what was then called the Environmental Defense Fund. I was deeply concerned about the climate issue, but wasn't sure how to stimulate government interest.

In October 1985, the UN sponsored an international meeting of scientists on climate change in Villach, Austria. Its conclusion: Increasing concentrations of greenhouse gases could cause an historic rise in global temperature. This was the first international scientific consensus on climate change and an important turning point, but the key question was, "Could this scientific concern be directed toward leveraging government action worldwide"?

To address this question, the UN's Environment Program (UNEP), the World Meteorological Organization (WMO), and the International Committee of Scientific Unions created an international scientific panel called the Advisory Group on Greenhouse Gases (AGGG). Perhaps AGGG's main accomplishment was to provide official auspices for a more activist group of experts that included George Woodwell, now retired as director of the Woods Hole Research Center; Bill Clark, now at Harvard's Kennedy School; Gordon Goodman, now retired as director of the Stockholm Environmental Institute; Jill Jaeger, also then at the Institute; and me.

Our group hoped to engage governments and the public in a chain of events that would culminate in a "framework convention", a type of treaty suggested by the Villach participants. To this end, we organized or helped to plan a series of science and policy meetings between 1987 and 1990, including the highly visible World Conference on the Changing Atmosphere, sponsored by the Canadian government and held in Toronto in the summer of 1988.

Public concern in the US over climate change was rising at the time for many reasons, including the unusually hot summer in the US in 1988, a sustained drought in parts of the country, the Congressional testimony of NASA's James Hansen pointing to a human influence on climate, and a series of unrelated but salient environmental problems, including the ozone hole. Also, other groups besides ours, in the US and abroad, were pressing for action on the climate front.

Following on the Villach meeting, Dr. Moustafa Tolba, the head of UNEP, had written to then US Secretary of State George Schultz calling for international action to address climate change. This led to considerable discussion within the US government, WMO, and UNEP. The US government decided that, as a first step, it could support an intergovernmental scientific panel to assess climate change. Facilitated by US support, the IPCC was established at the end of 1988.

IPCC's first chairman was Swedish climatologist Bert Bolin, and its second was atmospheric scientist Bob Watson, who helped develop the assessment process for the ozone depletion problem on which the IPCC was partially modeled. In the rejoicing over the award of the Nobel Peace Prize, I hope that the contributions of Tolba, Bolin, and Watson are remembered.

US support was probably critical to IPCC's establishment. And why did the US government support it? Assistant Undersecretary of State Bill Nitze wrote to me a few years later saying that our group's activities played a significant role. Among other motivations, the US government saw the creation of the IPCC as a way to prevent the activism stimulated by my colleagues and me from controlling the policy agenda.

I suspect that the Reagan Administration believed that, in contrast to our group, most scientists were not activists, and would take years to reach any conclusion on the magnitude of the threat. Even if they did, they probably would fail to express it in plain English. The US government must have been quite surprised when IPCC issued its first assessment at the end of 1990, stating clearly that human activity was likely to produce an unprecedented warming.

The IPCC's first assessment laid the groundwork for negotiation of the UN Framework Convention on Climate Change (UNFCCC), signed at the Earth Summit in 1992. In a sense, the UNFCCC and its progeny, the Kyoto Protocol, were unintended consequences of the US support for establishment of IPCC – not what the Reagan Administration had in mind!

Climate models are usually run far into the future, projecting temperature changes to the end of the century. Over the long term, the effects of greenhouse gases overwhelm all other factors. But climate can have substantial "short-term internal variability" – for example, temperature shifts due to El Niño and La Niña. Climate models have never been able to predict this internal variability – until now.

A paper in today's issue of Science ("Improved Surface Temperature Prediction for the Coming Decade from a Global Climate Model") describes a new and improved climate model that predicts both greenhouse warming and internal climate variability. The model's hindcasts are substantially better than earlier model results. (For more on hindcasts, see the post "Climate Models: How Good Are They?").

When the authors ran their model into the future, they found that internal variability would offset global warming until 2008, but the new model (like older models) predicts significant warming during the coming decade. At least half the years after 2009 are predicted to exceed the warmest year currently on record.

So while the improved predictability of short-term variability is welcome, the long-term picture remains the same. The world is getting warmer.

I've been reading a great book called Uncertain Science… Uncertain World by Henry Pollack – a readable and engaging discussion of decision-making in the face of uncertainty. Pollack argues that decision-makers use uncertainty as an excuse for inaction, when in fact it should be a stimulus for creativity and progress.

How sure do you have to be that something will happen to act on the possibility?

We don't give it much thought, but we take action in the face of uncertainty all the time. We're not sure we'll get into a car accident, but there's a small chance we will so we wear our seat belts. And though we may never need it, we buy major medical insurance. We act on these possibilities, though they're unlikely, because the consequences, if they occur, are severe.

Yet scientists are held to a different standard. Some people feel that if scientists aren't 100 percent certain about something, there's no need to take action – even when there is a 90 percent chance that inaction will lead to catastrophe. Why?

Bill used a great analogy to explain this in a Webcast for teachers in Tennessee. (The section on scientific uncertainty begins about 3 minutes into the video.) He says that some people think of scientific knowledge as a house of cards – if one piece is taken away, the whole house comes down. That is, one uncertainty about climate change means none of the science can be trusted.

In fact, scientific knowledge is more like a jigsaw puzzle than a house of cards – a jigsaw puzzle where you don't have the box top. As you fit the pieces together, a picture begins to emerge. You may not know all the details, but enough pieces are in place to leave no doubt what the big picture is. That's where we are now with climate change. The big picture is clear, and the debate is only about individual pieces here and there. Just because scientists don't know everything about a particular topic doesn't mean they don't know anything about it.

In our everyday lives we act based on incomplete information as a matter of course – to the point that we don't even think about it. But for scientists, uncertainty is top of mind. They're trained to notice what's certain and what's not so they can design useful studies. That's why they spell out in such exquisite detail what they don't know about any given topic. And that's why the IPCC report (indeed, any scientific report) uses such careful language. Sometimes, all that careful language can obscure aspects of a topic that are settled.

Unlike a car accident, which is serious but unlikely, global warming is both serious and likely. In fact, the clear picture that has emerged from decades of research is that it's already happening. We must act now to reduce greenhouse gas emissions. The challenge facing us can seem overwhelming, but we can turn this around.  

So the next time someone tells you that global warming isn't a certainty so there's no reason to act, ask them what the probability of an accident has to be before they'll wear a seat belt.

Stephen Colbert once quipped, "It's not that I don't believe in climate change, it's that I don't believe in climate. Have you ever heard anyone say, "How's the climate?" No! They say, "How's the weather?""

People often confuse climate and weather. They wonder how scientists can reliably predict climate 50 years from now when they can't predict the weather a few weeks from now. The answer is that climate and weather are different, and it's easier to predict climate than weather.

Weather is a short-term, local phenomenon. Climate is the average weather pattern of a region over many years. I may not be able to predict the weather in New York City on December 15, but I can predict with confidence that it will be colder than it is today, in mid-July.

A climate model could make the same prediction without a single past temperature reading. Basic orbital mechanics tell us that the northern hemisphere is colder in winter than summer.

As I explained in my previous post, a climate model is a mathematical description of the physics and chemistry of the climate system – for example, how heat is transferred from one place to another. The inputs to the model are things like solar radiation, volcanic eruptions, and human-produced greenhouse gas emissions. Based on these inputs and the laws of physics, the model predicts temperature, precipitation, and other aspects of climate.

Which brings me to how we know the models are credible.

What if the model inputs were actual observations from a time period in the past where we have full climate measurements? If the model is any good, it should accurately "hindcast" what we know the climate conditions were. In fact, hindcasting is the technique scientists use to evaluate models. If a model can accurately hindcast, we can have some confidence in its forecasts of the future.

In the graph below, the yellow lines show 58 temperature hindcasts from 14 different climate models. The thick red line is the average of all the hindcasts; the black line shows actual global temperature over the past century. Note how close the hindcast average is to actual temperatures. The models do a very good job of predicting 20^th century climate.

Source: IPCC AR4 WG1 Figures [PPT file]

Why do we need 14 different models? Models vary in their complexity – how many factors they take into account. A simple model can take just a minute to run, but a complex model requires serious computing power and time. Even complex models differ in the factors they consider.

And how is it that the same model can produce different hindcasts? This has to do with the nature of the grid I described in my previous post. The atmospheric cells used to predict global climate are larger than some of the inputs to the model – for example, clouds. The way scientists take these influences into account is by "parameterizing" these "subgridscale" phenomena – that is, they make an estimate. The different hindcasts come from different parameter assumptions.

Averaging the predictions of different models and different parameters usually gives a better prediction of real-world observations than any one model. The averaging minimizes any bias there may be in a particular approach.

The issue of what to input when forecasting – for example, the level of carbon emissions to expect – can be tricky. Scientists thus look at different scenarios. For example, in the graph below, A2 is the most fossil-fuel intensive scenario and B1 the least. The scenarios [PDF] are based on "storylines" representing different demographic, social, economic, technological, and environmental developments (none of which includes initiatives to decrease greenhouse gas emissions).

Source: Figure SPM-7 in the summary of the latest IPCC report [2.9 MB PDF]

The Year 2000 line shows what happens if greenhouse gas concentrations stay at current levels. Temperatures will continue to rise slightly because it takes some time for carbon emissions to translate into global warming. Scientists call this the "warming in the pipeline".

Note that despite differences and imperfections, the models are unanimous in predicting future warming. To avoid dangerous climate change, temperatures cannot rise more than 2.3°F above what they are today. (For why, see Bill's post on How Warm is Too Warm?.) Even the best business-as-usual scenario ("B1" in blue) crosses that tipping point.

The implication is clear: we must cut our greenhouse gas emissions as soon as
possible. And now you know why scientists have confidence in these models!

Of everything in climate science, what seems to spark the most skeptical questions is our use of computer models. In this post and another to follow, I'll talk about exactly what these models do, and how they contribute to our understanding of global warming.

I'll start with why we use models in the first place. We want to project what will happen to our climate in the future – will it be warmer? How much warmer? Will it change in different ways in different places? Climate models use our knowledge of how the climate system works to calculate what different emissions scenarios mean for the future. Here's how the models are built.

General Circulation Models, or GCMs, are computer programs that use basic physics and chemistry to calculate properties of the atmosphere and ocean, such as temperature, precipitation and sea level.

GCMs represent the Earth’s ocean, biosphere, and atmosphere in three-dimensional cells. The models stack ocean and atmospheric layers in grids across the Earth’s surface. An example schematic of atmospheric cells is shown below. The models use differential equations to calculate transfers of radiation, heat, carbon, water, and other substances between cells.

A Coarse Example of Atmospheric Cells

Figure from the Australian Bureau of Meteorology

If you want to dig into the nitty-gritty on GCMs, a good resource is Chapter 8 of the IPCC report [6.4 MB PDF] and its hefty supplement [40.9 MB PDF].

How we use a GCM depends on its complexity. The simplest models take less than a minute to complete a 100-year simulation. A more complex, high-resolution model can simulate complex phenomena such as regional weather extremes or atmospheric dust transport, but using these kinds of GCMs requires substantially more computing power and time. Documentation and data from all of the GCMs used in the latest IPCC report are available here.

To run a GCM, we need to give it input. This information includes solar radiation, volcanic emissions and human-produced emissions of greenhouse gases. We have this information for the 20th century, but of course we don’t know what emissions will be in the future. Scientists deal with that uncertainty by using a range of emissions scenarios.

Some emissions scenarios are “fossil fuel intensive”, with emissions continuing to increase (for example, Scenario “A2” shown below in red). Others assume that greenhouse gas emissions decrease at various rates over time. For example, emissions cuts in Scenario “B1” (blue) are steeper than those in “A1B” (green). As shown in the graph below, using different scenarios results in different predictions for global temperature change.

This is Figure SPM-7 in the summary of the latest IPCC report [2.9 MB PDF]

Each scenario has a thick line with some shading on either side of it. The line represents the average of several model runs. The shading shows the range of temperature predictions from all the models.

All of these models were given exactly the same inputs — so why don’t they give the same results? Some of this has to do with the different levels of complexity from model to model. Some of the spread also comes from uncertainties in various factors such as the carbon cycle (the rate at which soils and plants store or release carbon), climate sensitivity (the amount of warming for a given amount of greenhouse gas) and cloud formation (which can lead to warming or cooling). Each model deals with these factors slightly differently, which leads to variations in their predictions.

These uncertainties lead to the most common question about climate models — How accurate are they? — which is the topic of part two. Stay tuned!

Everybody knows about Abraham Lincoln’s Emancipation Proclamation and Gettysburg Address; they are a big part of why Lincoln's birthday is honored. Most people don't know that Lincoln also established the National Academy of Sciences (NAS).

Established by the U.S. Congress and President Lincoln in 1863, the NAS charter states that "the Academy shall, whenever called upon by any department of the Government, investigate, examine, experiment, and report upon any subject of science."

Since Lincoln’s time, the National Academy of Sciences has been joined by the National Academy of Engineering, the Institute of Medicine, and the National Research Council. To this day, Congress relies on these institutions for objective and non-partisan advice. In 2005, the White House called the Academies’ work “the gold standard of independent scientific review.” In light of this, it's interesting to note what the National Academy of Sciences has to say about global climate change.

In 2005, the NAS joined with the science academies of ten other countries to produce the "Joint science academies' statement: Global response to climate change". The statement says, in part, "The scientific understanding of climate change is now sufficiently clear to justify nations taking prompt action. It is vital that all nations identify cost-effective steps that they can take now, to contribute to substantial and long-term reduction in net global greenhouse gas emissions."

Even the NAS agrees – the time for action is now.

Oh, and in the interest of full disclosure: I am a member of the National Academy of Sciences – elected in 1998. (See the NAS site for how members are nominated and elected.)

But some folks are not so sure about this IPCC thing. They want to know: "What is the IPCC anyway, and why should I trust what they have to say?" Our good friends at the Wall Street Journal tell us not to trust the IPCC, it's written by a bunch of "policymakers." (See the editorial.)

Not so fast. Here's what the IPCC really is.

IPCC stands for the Intergovernmental Panel on Climate Change. It was established in 1988 by the World Meteorological Organization and the United Nations Environment Programme. It is open to all members of these organizations, including the United States. IPCC assessments take 5 or 6 years to produce. The 2007 report is their fourth assessment. The last one was released in 2001.

The summary released last week is actually the first of three reports. This one, by "Working Group 1," reviews the best available scientific information about the climate system.

Here's why you should take the report seriously:

• The report is not about policy or politics – it's just about the science. In fact, IPCC is expressly barred from making policy recommendations.
• It was prepared by more than 2,000 scientists from all over the world working together for years. The conclusions were reached by a consensus of all scientists involved. There isn't a minority or dissenting report.
• After the scientists reached consensus, their assessment was subjected to extensive review, by hundreds of independent scientists as well as all the sponsoring governments. The report could not be released until all governments, including the United States, signed off.
• If anything, IPCC assessments are conservative. One reason is the requirement that all the scientists involved reach consensus and all the governments sign off. Another is the time it takes to produce. This latest assessment was only based on scientific studies completed before January 2006, so it did not include the important new findings of 2006. These include studies documenting accelerated melting of the Greenland ice sheet and studies indicating that sea levels will rise even higher than previously thought. So when the IPCC says there is a 90 percent probability that global warming is caused by human activity, they are not exaggerating. In fact, it's on the low side.
• Finally, the IPCC assessment team was led by Dr. Susan Solomon of the National Oceanic and Atmospheric Administration. I know Susan; she is a world-class scientist who insists on the highest standards. She's also a winner of the U.S. National Medal of Science. Her agenda is science and only science – there is no politics in her work, period.

So the IPCC isn't a conference, nor is it the opinion of a group of hand-picked scientists with an axe to grind. And it isn't some international cabal out to get the United States. We are a member nation of the IPCC and our government has signed off on what the Bush administration called a "landmark" report (see the administration press release).

This document is for real and we ignore it at our own peril.