Climate change: Who is a climate scientist?

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Climate change: Who is a climate scientist?
Some like it hot. Click ‘play’ to watch a warming world, from Marilyn Monroe to Mitt Romney. Temperatures represent 5-year running averages between 1950 and 2012, so we can see climate trends instead of climate extremes.
Imagery: NASA/GISS

As storms rage, seas rise, and ice and permafrost melt, the planet sets a steady procession of temperature records. So it’s getting harder to deny the reality that human actions — mainly burning fossil fuels — are changing the climate. Still, when asked, some politicians reiterate, “I am not a scientist.”

That disregard for science flies in the face of the near-universal acceptance of global warming and climate change among scientists, not to mention the logical linkage between the melting, droughts, heat waves, catastrophic storms and record rainfalls and snowfalls to gases that trap heat in the atmosphere.

Here’s one gauge of the growing scientific alarm, from the U.S. National Research Council (our emphasis added):

The rate of climate change now underway is probably as fast as any warming event in the past 65 million years, and it is projected that its pace over the next 30 to 80 years will continue to be faster and more intense.1

Americans seem to be getting the message. On Jan. 31, the “New York Times reported that “An overwhelming majority of the American public, including half of Republicans, support government action to curb global warming, according to a poll conducted by The New York Times, Stanford University and the nonpartisan environmental research group Resources for the Future.”

If politicians are not paid to be scientists, neither are they paid to ignore the obvious. As the ramifications of climate change broaden, we got to wondering: who are the scientists who study the causes and effects of climate change?

To sample the range of approaches, we put out some feelers at University of Wisconsin-Madison. It’s not just weather people who are exploring the biggest environmental problem of all.

A focus on the Arctic

Steve Vavrus is a climate modeler who focuses on the Arctic – where, as predicted, the fastest warming on Earth is taking place. The term “modeler” evoked the time-worn allegation that climate models are no more reliable than weather forecasts, so we asked why we should trust climate models? “Model evaluation and improvement is a big part of climate modeling nowadays,” said Vavrus, a senior scientist at the Nelson Institute Center for Climatic Research at UW-Madison. “There is a lot more communication between people who make measurements and observations, and modelers who are trying to improve accuracy of climate models.”

The basic way to test and improve models is to start them with data from, say, 1930, and ask whether they produce:

Modern, average temperatures and precipitation

Reasonable day-day or year-year variability/p>

Broader trends over longer periods

Getting accurate data for the globe is always a challenge for climate scientists, Vavrus says. “If you have a model simulation, you want to know if the output is accurate.” The answer will vary depending on the data used to start the model and verify its predictions.

Satellite image comparison of the Arctic showing Arctic sea ice decline between 1979 and 2012 when it covered about a third of its previous 1979 extent.
A satellite comparison of late-summer Arctic sea ice coverage between 1979 and 2012, when the area of Arctic ice hit an all-time low.

The biggest result on Arctic climate in the past decade is the dramatic, faster-than-predicted loss of sea ice. “The summer of 2007 caught everybody by surprise,” Vavrus says. “I was shocked when I saw the satellite image: It looked like the output of a climate model simulation for the end of the century. And every summer since 2007, sea ice has been less than the year before.”

Vavrus is studying how the loss of sea ice and the rapid Arctic warming affect weather in regions to the south, such as the Midwest. “It’s a controversial subject, but I think the question is not whether the change in the Arctic affects atmospheric patterns elsewhere, but where and how they are having effects.”

A climate scientist gestures in front of a climate tower in a young forest.
Ankur Desai at a 27-meter-tall flux tower near Minocqua, Wis. on Sept. 17, 2011. Desai studies the movement of carbon dioxide and methane between the atmosphere and land-based ecosystems; the tower provides continuous measurements for gases in the atmosphere. “If we want a credible policy to tackle climate change and reduce greenhouse gases, we need to know where the carbon is going,” Desai says.
Photo: Bryce Richter / UW-Madison

Minding the carbon

Carbon is the atom of life: The shape-shifting champion of the periodic table can form a bewildering array of molecules. It’s also the armature of the major greenhouse gases: carbon dioxide and methane (CH4).

Carbon is also the namesake of Ankur Desai’s field: carbon cycle science. That’s the study of how greenhouse gases enter, change and leave the atmosphere.

The climate-altering pollutants from smokestacks and tailpipes eventually leave the atmosphere. Methane is oxidized into water and carbon dioxide in a century or so. Desai focuses on the terrestrial carbon cycle, the amount of carbon that goes into forests, soils and wetlands. Desai, an associate professor of atmospheric and oceanic sciences at UW-Madison, says that for every ton of carbon released by fossil fuel, half a ton is stored in land and the ocean.

Carbon storage “is a service that the ecosystem provides that can buy us time if we are interested in addressing fossil-fuel emissions or effects,” Desai says. But carbon storage is not permanent.

The biggest surprise from carbon-cycle science, Desai says, is the size of the “carbon pools” in the soil. “In the tropics, we have underestimated just how efficient soils are in taking up carbon. Greenhouse gases are the drivers of climate change, and being able to measure them in the atmosphere is fundamental.”

illustrated diagram shows Ross Ice Shelf location on earth, plus direction of ice flow, and heating of water underneath the shelf in the ocean, also labels: grounding line ocean floor, continental shelf, ice sheet and sea ice
Warmer ocean water lapping at the underbelly of floating ice shelves and glaciers on West Antarctica erodes the contact between land surface and the massive ice sheet, known as the ‘grounding line.’ Destabilization of these ice buttresses raises concerns of future collapse of the West Antarctic Ice Sheet into the southern ocean, and, when it starts, there may be no stopping it.
Diagram: S.V. Medaris for The Why Files.

Ice: Carbon’s icy accounting

Two glaciologists enjoying the view on an ice-less stretch of the frozen Antarctic dessert.
Shaun Marcott (right) collecting rock samples for dating glacial deposits in the Dry Valleys of Antarctica. The frozen continent is one of the best records of past atmospheres and climates.
Photo: Shaun Marcott

Shaun Marcott reads messages about ancient climates inscribed in ancient ice. Ice originates as snow, which contains air. And so ancient ice contains ancient air. “If you want to look 10,000 or 20,000 years back, the only way to do that directly is with an ice core, which actually contains air from the prior atmosphere,” says Marcott, an assistant professor of geoscience at UW-Madison. “When I measure CO2 2 from 20,000 years ago, I actually have air from 20,000 years ago.”

And those ice cores show fast increases in temperatures and carbon dioxide. “We are seeing 1 part per million rise per decade in the past, but carbon dioxide in the modern atmosphere is changing much faster, at about 2 ppm per year,” Marcott says.

Even though the past rate of carbon dioxide rise is just 5 percent of the current rate, the ice ages were quickly terminated, Marcott says.

Marcott says the most significant findings in polar climate over the past decade are rising sea level and the decline of ice sheets on Greenland and Antarctica.

These factors are “inherently linked,” he adds. Because these ice sheets store most of the water that’s not in the ocean, sea level falls when ice sheets expand during cold eras. When the climate warms, ice melts and sea level rises. “We have been realizing that changes in sea level have happened very quickly,” Marcott says, “and this really means the ice sheets have responded in the past much faster than anticipated.”

Until recently, climate scientists discounted the possibility of quick melting in the Antarctic ice sheet, since air cannot warm it fast enough. Now it’s clear that warm ocean water is eroding the ice from below, raising the potential for rapid collapse that could “uncork” the masses of ice further inland, accelerating their slide into the ocean. “It’s like knocking the legs out, and this is something we did not anticipate 15 years ago,” Marcott says.

Just as modern research shows rapid melting in ice sheets, “Research on the past is telling us the same thing, Marcott says. “Those together make a powerful case that we need to be concerned about this ice.”

A cloudy picture — still

Clouds have long been the bane of climate modelers. They come, they go, and their effects can be topsy-turvy:

Clouds near the ground cool the planet by reflecting short-wave solar energy to space

High-level clouds warm Earth by reflecting long-wave radiation back to the surface

Two images of the western Hemisphere showing red over much of North America during summer, indicating warming clouds, then blue during winter, indicating cooling. The tropics are red despite the seasonal difference, and so is South America, except for a shift to blue over the Andes during Southern Hemisphere winter.
Clouds warm the planet in some places, and cool it in others, largely depending on altitude. “Increased cloud cover in a warmer climate might cause either positive or negative feedbacks,” says atmospheric scientist Tristan L’Ecuyer. “Those locations also vary depending on the time of year, especially across a mid-latitude region like the continental United States.” Blue = low-level (cooling) clouds, red = high level (cirrus, warming) clouds.
Courtesy Tristan L’Ecuyer, University of Wisconsin-Madison

Tristan L’Ecuyer, assistant professor of atmospheric and oceanic sciences at UW-Madison, looks at how clouds affect the radiation budget — the balance of incoming and outgoing radiation that is the fundamental equation of global warming.

With more energy, and therefore more moisture in the atmosphere, clouds are likely to increase as the climate warms, but the evidence is disputed, L’Ecuyer says. To understand how changes in clouds will play out, you need to talk about changes in their timing, prevalence, density and altitude.

Although long databases trump short ones in the climate business, satellites may drift and cover different regions, and all satellites die. If replaced, the new instrument may have a subtly different calibration.

To sidestep these snafus, L’Ecuyer

examines shorter records from single satellites; and

compares summer and winter clouds. By calculating the change for each degree C, “you get an idea how a smaller warming, like that due to carbon dioxide, will affect clouds,” L’Ecuyer says.

Theoretically, clouds can lead to positive feedback (warming increases clouds which increase warming), or negative feedback (warming increases clouds which slow the warming).

The uncertainty whether any feedback will be positive or negative “is leading to a spread in the predictions of future climate,” L’Ecuyer says. Clouds are extremely unlikely to reverse the overall warming trend, “so we are not talking about cooling, but about how much warming: will it be 2° C or 10 ° C?”

Global climate models are “downscaled” to project conditions over the Great Lake region, comparing the 1990s to those expected by the end of the 21st century (rollover image).
First: map of temperature and rainfall change over the Great Lakes showing uniform warming and increased rainfall, mostly in the east. Second: warming at the end of the century will be even greater in the north, and the precipitation pattern will be exaggerated.

Eye on the Great Lakes: Michael Notaro

How will the Midwest, a region dominated by the world’s largest fresh-water bodies, fare as climate changes? The answer lies in regional climate models — smaller offshoots of the global models first used to anticipate the warming era.

A dozen climate models forecast that average temperatures in Wisconsin will rise 6° F. by 2050, says Michael Notaro, associate director of the Center for Climatic Research at UW-Madison. By century’s end, average Wisconsin temperatures are expected to rise another 2° and winter will be about 10° F warmer.

This would not seem helpful to the ski and snowmobile industries, but Notaro says lake effect snow downwind of the Great Lakes, in places like Northern Wisconsin and the eastern shore of Lake Michigan, is already rising.

Lake effect snow is fed by heavy evaporation from the warm, relatively ice-free surface of the Great Lakes. In Syracuse, N.Y., lake effect snow has roughly doubled over the past century, Notaro says. Eventually however, as warming continues, the heavy snow will turn to heavy rain.

We reminded Notaro of the old skepticism about global climate models: If models can’t agree, why should we trust any of them?

Notaro responds by saying, essentially, “Look at the record.” Before a model is taken seriously, it must “reproduce what happens on the global, continental scale fairly well.”

Diagram showing three columns: left shows the historic rate of extinctions that is between 0.1 and 1 species per thousand species per millenium, middle shows the current rate at around 100, right shows future predictions between 1,000 and 10,000.
The rate of recorded extinctions today are about 100 times higher than the rate in the fossil record. Scientists see a role for climate in some extinctions, among many other factors.

Historic data on the real climate “are consistent with the models; they show warming, mostly in the cold season,” he adds. “The minimums are warming more than the maximums, we are getting more extreme precipitation events. We have less ice. These are all in the observations, and in the models, there is no inconsistency. A lot of it is basic science on how greenhouse gases affect the radiation budget. It’s pretty logical.”

The core that keeps score

As scientists continue to document physical and biological responses to current global warming, some are exploring the consequences of past warming.

Jack Williams, a UW-Madison expert on global warming and ecological responses to past and future climate change, gets data from lake sediments. Once grad students have slaved long hours at the microscope to identify the pollen in that muck, they can reconstruct plant communities that vanished thousands of years ago.

Williams, who directs the Center for Climatic Research, says pollen samples show the presence of spruce trees in Southern Wisconsin 15,000 to 20,000 years ago, when the climate was 3° to 5° C cooler. Today, those spruces live in Northern Wisconsin.

Globally, soil and plants store about one-quarter of the carbon entering the atmosphere, which slows warming. But some scientists predict that over the century, ecosystems could become net sources of carbon dioxide. “It’s a big uncertainty with big societal implications for the rate and consequences of climate change,” Williams says. “There is a critical need for improved models” to simulate the next few centuries, “and we need observational data.”

What is already clear, he adds, is that “The ecological system and species are really sensitive to climate change. We are going to see a lot of ecological turnover, species coming and going. In the best case, species will shift range, but the forest in Northern Wisconsin is not going to be the forest we had in 1900. Or we will see species going extinct if they can’t cope with change, disperse or migrate.”

Photo of three researchers using a metal tripod and a steel pipe mechanism to hoist columns of sediment from an Alaskan bog.
A WhyFiler Kevin Barrett demonstrates a ‘peer reviewed’ technique for collecting peat bog sediment, in Juneau, Alaska. Cores extracted from sediment carry biological clues to past ecosystem and climates. Hopping on the coring machine drives the cylinder into the bog.
Courtesy Kevin Barrett, 2011

Studies of the recent ice age show that “a 5°C temperature change truly transformed the Earth system,” Williams says. “Species shifted thousands of kilometers and ice sheets melted away. What seems like a small number can have a large ecological effect.”

History of the forest

Beyond pollen, other remnants of vanished plants can document long-gone conditions. Sara Hotchkiss, an assistant professor of botany at UW-Madison, looks at carbon isotopes in remnants of a wax that plants made to protect their leaves from drying out.

When moisture is short, plants preserve it by closing pores in the leaves. That causes them to metabolize more of a heavier carbon isotope, which shows up in wax created by plants to fight droughts. Isotopes “tell us climate history in a way that is independent of vegetation history,” Hotchkiss says.

Using evidence from pollen, Hotchkiss is locating past upper limits on the cloud forest on Maui, Hawaii. The upper limit seems to move down during droughts, she says, shrinking the forest. “We have not found a time in the past 7,000 years when the upper limit was lower than at present. It’s pretty speculative, but it’s probably as dry as it has been in the last 10,000 years” in Hawaii.

The upper limit of the cloud forest matters, Hotchkiss says. “The cloud forest has the most intact native vegetation and hardly any invasive species, which is really weird in Hawaii. It’s the most important habitat for native Hawaiian birds, which are totally under siege.”

And yet if further drying accompanies climate change, that upper limit could move further down the mountains, shrinking the habitat for native birds, even as mosquitoes and the avian malaria they carry continue moving up. The result could be further extinction on islands already infamous for the disappearance of species.

The genetics of climate

Modern responses by ecosystems and organisms to rising temperatures and associated phenomena of climate change are changing behavior and evolution:

plant and animals are moving toward higher altitudes and the poles;

new rhythms of animal migrations and plant flowering reflect the altered timing of the seasons; and

scientists are associating climate change with evolution, meaning genetic changes in plants and animals.

“Natural selection is happening now, in response to climate warming,” says Sean Schoville, an assistant professor of entomology at UW-Madison. Schoville studies the effects of climate change on the genetics, populations and movement of alpine insects, including butterflies, ground beetles and the rare ice crawler.

Photo of a tawny and long insect creeping across snowy ice crystals.
Ice crawlers, native to western North America and northeast Asia, forage for food at night in snowy mountains. Because they freeze to death below – 6° or -8° C., they retreat beneath the snow, where temperatures are more stable. Like many mountain organisms, ice crawlers tend to be highly local: “If you go from one mountain range to another, you find a distinct, isolated population,” Schoville says.

Genetic research builds on new information about past ecosystems, Schoville says, based on data from fossil pollen, marine organisms and gases from ice cores that reconstruct past temperatures and atmospheres. “People have collected this wonderful paleoclimate data that we use to make predictions on what the habitat might have been like, what species were living there.”

Even though the insects he studies do not fossilize well, Schoville can visualize their likely past by studying:

existing fossils to get a picture of past ecosystems;

the genetics of modern populations, which show a “genetic bottleneck” caused by small numbers during the last glacial cycle; and

genes that helped adaptation to climate change.

Alpine insects, he says, “tend to have very conserved genetic responses to temperature stress, whether cold or heat. It’s usually the same repertoire of genes that is turned on, and it does not change much among species. So what you find in one species usually applies to another.”

A climate for food?

To grasp the lockstep link between climate and food, consider the Sahara: A few thousand years ago, today’s archetypal desert was a greenbelt. So climate necessarily intrudes on agronomy, the science of crop production. Via email, Chris Kucharik, an assistant professor of agronomy at the Nelson Institute at UW-Madison, elaborated on this link: “We are interested in how changes in mean climate and weather variability impact crop growth and yields, crop management decisions (for example planting dates, dates of flowering, harvest dates), weeds (types and growth), and soil resources (for example nutrient availability and erosion).”

To understand the interaction between weather and various cropping systems, agronomists use field studies and data on harvested acreage and yields. “Field trials for current and new hybrids across a variety of soil types and climates tell us how they perform/respond to different weather conditions and management options (for example planting dates, planting density, fertilizer applied, weed management and soil tillage options),” Kucharik wrote.

Photo of a young man and his family tilling a dry field with short hoes.
Overgrazing, over-cultivation, deforestation and poorly planned irrigation systems accelerate land degradation, and climate change exacerbates the problem. The process of desertification has destroyed vast landscapes across Asia, Africa and the Americas.
Photo: IFAD

Agricultural adaptation is ageless; people have been breeding crops to suit current conditions for at least 10,000 years. “In the science of plant breeding and plant genetics, new hybrids and crop varieties are constantly evolving to be able to better withstand extreme environments such as heat and drought, and pests and disease,” Kucharik wrote.

If climate changes slowly, it may be possible to “give farmers the tools they need to continue to adapt,” Kucharik added. “If large, abrupt shifts in climate were to occur, that would be much more challenging in many regions if it meant growing new crops, needing different equipment, or entirely different management approaches.”

Unfortunately, Kucharik says the most significant finding in his field in the past decade suggests limits to adaptation: “In some countries, climate trends have been large enough to offset a large portion of the increases in average crop yields that arose from advances in breeding and agronomic practices. Therefore, we are having a hard time in some places combating detrimental effects of climate change on food production with new scientific advances.”

A climate for closing

As we conclude our partial survey of scientific approaches to climate change, we suspect that cynics will mock the deep and broad focus on climate as egg-headed efforts to embark on a climate-change gravy train. But there’s an alternative opinion: that these are seeing attempts by concerned, educated experts to unravel the biggest threat to the only planet that assuredly harbors life.

– David J. Tenenbaum

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Kevin Barrett, project assistant; Terry Devitt, editor; S.V. Medaris, designer/illustrator; David J. Tenenbaum, feature writer


  1. Abrupt Impacts of Climate Change: Anticipating Surprises, National Research Council, 2013, ISBN 978-0-309-28773-9,
  2. Stephen Colbert: “I’m not a scientist.”
  3. An exploration of Greenland stratigraphy and the scientists unearthing the mysteries.
  4. Climate change on pace to occur 10 times faster than any change recorded in past 65 million years, Stanford scientists say.
  5. The Velocity of Climate Change.
  6. An up-to-date monitor of Arctic sea ice.
  7. A Ted talk by Allan Savory on reversing desertification.