Bercovici, Pagani, Park and Wettlaufer: Perspectives on Climate Change

This week begins the United Nations Climate Change conference in Copenhagen (the “COP15”), following the controversy of stolen emails from the University of East Anglia’s Climate Center. Both events have inspired a flood of news stories, editorials and blogs. Although climate change remains one of our most urgent contemporary issues, it is wise to step back and view the big picture of what scientists do and do not understand about the Earth’s climate system and future climate change.

By its nature, scientific inquiry is highly competitive. “Scientific consensus” describes a state of shared knowledge in which each researcher is skeptical of the work of all other researchers. All ideas, interpretations, and data are aggressively cross-examined, debated and dissected to a degree rarely encountered in other professions. Scientists challenge prevailing ideas and concepts, and are often motivated to reveal the fallacy of commonly held perceptions. Climate science is no exception, and given the high-stakes nature of the topic, results are more highly scrutinized by scientists and policy makers than in many other scientific disciplines. There is a massive international community competing over and examining climate data and models — the principal results and interpretations are not generated by a few groups in isolation.

Our broad understanding of Earth’s climate system is based on observations, experiments and models by atmospheric chemists, meteorologists, glaciologists, solar and planetary physicists, oceanographers, geologists, geochemists, biologists, paleontologists, paleoclimatologists, paleoecologists and climate dynamicists. Finding agreement among these diverse groups is often as fractious as peace negotiations between warring nations. And yet, when it comes to the major issues of climate change, agreement exists.

We understand that Earth’s climate and temperature results from a complex interaction between solar heating, rocks, oceans, sea- and land-ice, water vapor, clouds, aerosols, biological processes, and greenhouse gases. Revealing the nature of these interactions and determining the direction of climate change as these variables are altered has required an unusually broad collaboration between scientists from a wide range of fields.

We know that the rise in carbon dioxide since the start of the Industrial Revolution has been the result of human activity, mainly from the combustion of fossil fuels. We know that carbon dioxide is a greenhouse gas, which traps heat and warms our planet. For an example of greenhouse warming, one need only look at our sister planet Venus, whose surface temperature makes rocks glow at night. Although Venus is closer to the Sun than is Earth, its extremely high surface temperature is mostly a result of its Carbon Dioxide-rich atmosphere.

An increase of Carbon Dioxide on Earth triggers other effects, called feedbacks, in response to increasing temperature. As surface temperature rises, more water evaporates from the ocean. Water vapor is another important greenhouse gas that causes more warming. Warmer oceans also do a poorer job of absorbing Carbon Dioxide from the atmosphere, while the melting of permafrost releases more Carbon Dioxide and methane, yet another potent greenhouse gas. All of these feedbacks lead to more surface warming. Warming also leads to a reduction of our “heat mirrors” — sea and land ice — which causes more sunlight to be absorbed by the surface of the Earth. This drives more warming and more ice melting, and so on. Positive feedbacks amplify the temperature effects of relatively small variations in Carbon Dioxide or other changes in the climate system, and it is for this reason that Earth experiences large swings in climate. It also warns us that the full effects of rising Carbon Dioxide levels do not occur overnight.

There are always complexities that are less well understood, like the role that clouds and aerosols (volcanic sulfates, bacteria, dust, soot) play in heating or cooling Earth’s temperature. These are important effects and are intensely studied.

We know that Earth’s surface temperature will continue to rise even if we immediately stop increasing Carbon Dioxide. The oceans are massive and take a long time to warm and catch up with surface temperatures, and as they do they absorb less and less carbon dioxide, while releasing more water vapor. However, there is no consensus as to how fast and how much warming will occur over the coming decades and century. This depends, to a large extent, on how much carbon is added to the atmosphere, as well as the “climate sensitivity to Carbon Dioxide”, which is the response of global temperature to the various feedbacks mentioned above. Determining the climate sensitivity is key to understanding how much warming we can expect. Magnitudes of climate sensitivity range from small to large and are different among the different computer models used to project future climate changes.

However, Earth’s history has something to say about climate sensitivity and the role of Carbon Dioxide as well. The reconstruction of Earth’s history reveals a story of slow and rapid climate change and clear evidence for immense variations in temperature. While most discussions in the popular press focus on the past 100 to a few 100,000 years and the precise relationship between Carbon Dioxide and temperature, it is informative to examine the full range of climate variations over millions of years.

Earth was, in fact, ice-free for most of its history. For example, Earth was much warmer and had no significant polar ice between 65 to about 34 million years ago. 55 million years ago, rapid, and massive releases of carbon acidified the oceans and warmed Earth’s surface about 5˚C above what was already a warm planet. At peak warming, about 50 million years ago, crocodiles roamed the Arctic amongst subtropical flora and fauna, even though the Sun’s intensity was lower than today. Much higher Carbon Dioxide during this time is revealed by various paleoclimate reconstructions, and subsequent global cooling is shown to have followed Carbon Dioxide decline.

Earth’s history tells us that the leading driver of climate change is the concentration of atmospheric carbon dioxide. Not the only driver, but the leading one. It also reveals that climate sensitivity to Carbon Dioxide is possibly much higher than discussed in policy-making circles. About 5 million years ago, Carbon Dioxide was as high or only slightly higher than 2009 AD values, and Earth reached temperatures 4˚C warmer than now, with sea levels tens of meters higher. The present-day location of Yale University was underwater.

Many lines of evidence and study tell us about the effects of carbon dioxide release. In the past, large increases in Carbon Dioxide corresponded to major warming events. It is unwise to think that today’s increase in Carbon Dioxide will, for some reason, produce a different outcome.

Mark Pagani is an associate professor of geology and geophysics, and a member of the Yale Climate & Energy Institute Executive Committee. John Wettlaufer is an A.M. Bateman Professor of Geophysics, Physics and Applied Mathematics. Jeffrey Park is a professor of geology and geophysics, and the director of the Yale Institute for Biospheric Studies. David Bercovici is a professor and chair of the Department of Geology & Geophysics, and the deputy director of the Yale Climate & Energy Institute.


  • Yale Science Undergrad

    Thanks for posting this. I think you’ve made a really good point about “climategate”: if it was possible to refute global warming, there would be so much fame and fortune to be gained from it, and scientists would jump at the opportunity. The idea that EVERY climate scientist has voluntarily foregone these rewards in a conspiracy to mislead the public is ridiculous.

    That said, I do have one thing to say about the issues raised by the “climategate” controversy. It looks like some scientists really did want to withhold data from the public– not because they were hiding a lack of warming but because they didn’t want the public to misinterpret the data. Should we maintain this “I’m an expert, take my word for it” attitude? Is the public qualified to look at the data? I’m interested to know what Yale scientists do regarding the publication of raw data from their papers.

  • Andrew

    The Climate Research Unit (CRU) in the UK was set up in 1971 with funding from Shell and BP as is described in the book: “The history of the University of East Anglia, Norwich; Page 285)” By Michael Sanderson. The CRU was still being funded in 2008 by Shell, BP, the Nuclear Installations Inspectorate and UK Nirex LTD (the nuclear waste people in the UK)

    This is important to know, for two reasons.
    Firstly, the key institution providing support for Global Warming theories and the basis for the IPCC findings receives funding from “Big Oil” and the nuclear power industry.

    Secondly, the research from the institution which is perceived to be independent publicly funded research, is actually beholden to soft money, CRU is in fact a business.

    The funders of the CRU are on the bottom of this page from their website:

    You can not put coal through a pipeline, nuclear power is expensive.

  • Andrew

    They can not hide the medieval warming period.
    It was much, much warmer during the medieval warming period than it is today.

    This is not so complicated

    There are Vikings that were buried (interred) in the permafrost in Greenland.
    The permafrost was not disturbed since it froze.
    It was not frozen when they were buried.
    I would call that warmer then today, a lot warmer.

    This was hundreds of years before the Industrial Revolution. They tried to hide this.

    The ironic thing is that this evidence of the medieval warming period is in a museum in Copenhagen.

    The Fate of Greenland’s Vikings February 28, 2000 by Dale Mackenzie Brown

    Also, the medieval warming period was global.

    Fraudulent hockey sticks and hidden data

    For a satirical look at the climategate computer programming (hiding the decline):
    Anthropogenic Global Warming Virus Alert.

  • Dave McK

    If you ask a scientist why nothing can move faster than the speed of light, he doesn’t tell you a terrible story about how koala bears will die if you don’t believe the theory is right, does he?
    The UN served this to the children of the world:
    This makes me very angry.
    CO2 is not a pollutant nor can it affect climate nor can you change it with 40 trillion dollars worth of lightweight, highly reflective Precautionary Headgear guaranteed to keep you cool in any weather. Get in on the derivatives bubble before it pops.

    Let’s examine some raw data, now, shall we, finally?
    From an 11 year old who doesn’t have a vanity blog: home schooled, I’ll bet a dollar. aggregation (with reference links)

    individual plots of raw australian data. more fraud revealed.
    She deserves the Pulitzer just like Woodward and Bernstein.
    Did you manage to find a synonym for the word HIDE than means anything other than HIDE- as in ‘HIDE the decline’?

    Norman Davies of propaganda
    Five Rules of Propaganda:
    1) endless repetition, repeating the same messages over and over with different variations and combinations
    2. Disfiguration: discrediting the opposition with slander and crude parodies
    3. Unanimity: presenting your point of view as if every right headed person agrees with it while smearing those who doubt it thanks using appeals of famous people, experts and so called consensus; hiding/ excluding others from the underlying basis / information of your position.
    4. Transfusion: manipulating the prevailing values of the public to your own advantage
    5. Simplification: reducing all facts into a comparison between ‘good and evil’ and ‘friends and enemies’

    What the fellows at East Anglia and elsewhere were doing was not science.
    When you actually put your own eyes on the raw data, you see what you see.
    Shall we have a look at the antarctic now?
    Scratch the surface – global warming is a fraud to the bone.
    It is Mann made.

    Jones ’stepped aside’, Mann ‘under investigation, Gore cancels Copenhagen speech, APA petition demands repudiation of the fraud, senators investigating on the hill…
    The news we all knew is even trickling in to CBS.
    The emails and programmer’s notes reveal the vast context of ten years of intellectual corruption. They were not doing science- they were disgracing it.

    You know- the globe has been getting warmer, you’re right. That’s why you can plant corn in Iowa and wheat in Kansas and why humans can live in Canada. The glaciers melted. I’ll have more of that, please.

  • BestTimesNow

    Here is the real story about climate history. IMHO (2 Posts-The 5 Stages of Earth)

    Water vapor is the most important greenhouse gas and has been responsible for most of the climate change for millions of years.

    Let’s look at progression of examples, starting with the warmest Earth, so you can see the effect on the planet. To keep things simple, we’ll set the composition of dry atmosphere, to the same as the present time, in all examples, so that we can see the effects of the water vapor in the air.

    Earth 1 – Water World

    We’ll start out with a hypothetical “Water World” type Earth, without any land. This will be the overall warmest Earth, with no ice caps at the polls.

    Why would it be warmer than the present day Earth? Water just rains out.

    Climate models are not required, just basic understanding and logic to find the answer.

    What’s different in “Water World”? All elevations are at sea level in “Water World”, so the height of atmosphere (greenhouse effect) is at a maximum level all over the world. The very humid, middle latitudes will be the warmest, with no relief, with the humidity. If it rains, the moisture in the air will be replaced very quickly. This part is similar to the very humid, present day, tropical ocean areas, but now covers 100% of the middle latitudes in “Water World”.

    Also, because of the insulating effect of the very moist atmosphere and unrestricted ocean currents, the middle latitudes (45N to 45S) will have a very constant, but warm, temperature with only a few degrees temperature swing between the daytime highs and the morning low temperature.

    The warm water from the middle latitudes will also mix with the polar oceans due to the unrestricted ocean currents, this will cause these regions to be much warmer than our present time polar regions, and there will not be ice caps at the poles. The air in the Polar Regions will also hold more moisture than our present time polar regions and will add to the greenhouse effect.

    Earth 2 – Cretaceous period type land mass

    Some low elevation continents are formed and cover 20% of the surface of the Earth. The land mass will disrupt the ocean currents and will allow the Polar Regions to cool. The middle latitudes will still be very humid (similar to Florida) because the most of the land mass will be at low elevations. Some of the larger continents will allow areas of lower humidity, which will allow some cooling at night. This planet Earth 2 will be cooler than Earth 1, but still very warm due to the greenhouse gas, water vapor.

  • BestTimesNow

    Part 2 (The 5 stages of Earth)

    Earth 3 – Paleogene (Eocene) period type land mass

    The continents now cover about 25% of the Earth and mountain ranges are forming. Although ocean currents are a little more restricted than Earth 2, it’s the larger continental areas, with mountain ranges that will allow Earth 3, to be cooler than Earth 2.
    As the prevailing winds pass over the mountains, the moisture in the air precipitates out, allowing for large areas of lower humidity, over some of the continents. The large areas of low humidity allow for even more night time cooling. Planet Earth 3 will be cooler than Earth 2, but still very warm due to the greenhouse gas, water vapor, but the water vapor is loosing its grip on keeping the Earth’s temperature elevated.

    Earth 4 – Pre Industrial Revolution

    The continents cover about 30% of Earth 4 and very high mountain ranges have formed. Ocean currents are very restricted, with the connection of North and South America and Europe, Asia and Africa forming large land areas. The vast land areas of lower humidity allow the middle latitudes to cool. Night time cooling is becoming greater over larger areas of Earth 4. (Just think back to Earth 1) Some of the higher mountain ranges remain snow capped all year long. Earth 4 is much cooler than Earth 3.

    Earth 5 – The present day Earth

    Due to the extreme population growth, humans are having an effect on the climate. What was desert and arid land has been converted into farms. The effect of irrigating millions of acres is similar to increasing the amount of the Earth that is covered with water. Most of the irrigation water is evaporated on a daily basis, which increases the greenhouse gas, water vapor and contributes to global warming.

  • Mike

    Dave and Andrew you are off your heads. What convinces you that after ten minutes of searching through pathetic blogs and the papers of attention-seeking morons you are better equipped to understand what is going on than hundreds of scientists in the IPCC? It matters not that the climate was warmer in the middle ages than it is now. What matters is that right now, things are heating up fast. This is shown clearly by the IPCC, the Stern Report on Climate Change, the missing snows of kiliminjaro or however the hell you spell it, and the fact that desertification across the equatorial zones of the world is spreading fast. Although you might enjoy having more days of beach time, if there’s a little more melt, several countries will go atlantis on us, bangladesh will be flooded, there’ll be hundreds of millions of refugees from sea water rises in India, water sources will be contaminated for hundreds of millions of others, and we cannot afford this. My grandchildren can’t afford this. Even if the chance of this destruction is 5%, that should be more than enough to move us to action on doing everything we possibly can to prevent it. It’s time we stopped shrugging off responsibility. The governments of the world have nothing to gain by hoodwinking the world’s public. And there is no way they could all work together to do so.

  • Yale 08

    Science derives its prestige from its reliability, and that reliability derives from its indifference to outcome and its success at canceling out the bias of the investigator by making the investigator universally interchangeable, so that any and all observers will observe the same thing. There’s a historical irony in scientists’ trading on the authority of their doctorates.

  • Kai

    Transparency is another problem. When Professors in Forestry are presenting themselves as scientists, for example, but even their faculty profiles say that they work on policy and don’t generate any data, you can imagine that it would be difficult for the average person to know the difference between that credentialed professor trumpeting moralisms and a true climate scientist who lurks elsewhere.

  • Tanner

    to Yale ’08

    Prestige is often the corruptor. Often when the marketing dept gets ahead of the end results. How many famous theories or discoveries been protected by its followers and the deciples of the “discoverer.” I’m sure there are a few at Yale. The fact that these zelots have changed the name from global warming to climate change tells us something doesnt it1

  • To #10

    Not all of the globe warms. While MAT goes up, circulation changes cause pockets to cool. So I’d call that name change an attempt to be more generally accurate and responsible.

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