This Week in Climate Science: Extreme Cold, Megafauna Extinction, and “Climate Change” or “Global Warming?”

By David Kroodsma

A loggerhead tutle. Credit: TvR/Flickr

Welcome to Climate Central’s weekly climate science roundup. This roundup summarizes noteworthy climate science studies published in the previous week, with a special emphasis on work that might not have been covered by major media outlets.

This week in climate science:

  • Global warming will not end extreme cold.
  • Scientists debate megafauna extinction and climate change.
  • Climate change will affect loggerhead turtle populations.
  • The commitments made in Copenhagen will have small economic consequences.
  • There is a need for better ocean acidification research.
  • Sea level rise and warmer temperatures threaten rice production.
  • Do people prefer “Climate Change” or “Global Warming?”
  • Climate change could weaken the ocean’s “biological carbon pump.”


Paper Title: Persisting cold extremes under 21st‐century warming scenarios
Journal: Geophysical Research Letters
Authors: Evan Kodra, Karsten Steinhaeuser, and Auroop R. Ganguly


Credit: Istockimage

The Gist: Global warming will not end extreme cold.

Summary: Climate models project warmer temperatures overall, and more frequent and intense heat waves as greenhouse gas emissions continue to rise. But what about extreme cold? Will cold spells disappear as average temperature increases?

The authors of this paper analyze the outputs of nine climate models using a scenario in which society continues to use fossil fuels in a “bussiness as usual” manner, and carbon dioxide (CO2) levels in the atmosphere more than double. They consider three indices of extreme cold for any given year: the average high temperature of the three coldest consecutive days, the maximum number of days in a row with frost, and the total number of days with frost.


They find that in the last decade of the 21st century, for a significant portion of the globe, about one out of ten years will still have cold events that are worse than the average coldest event for a year in the last decade of the 20th century. The authors conclude: “Our findings suggest that, despite a general warming trend, regional preparedness for extreme cold events cannot be compromised even towards the end of the century.”

Correspondence: Methane and megafauna
Journal: Nature Geoscience
Authors: Edward J. Brook and Jeffrey P. Severinghaus

Credit: thegaventas/Flickr

The Gist: Scientists debate whether the extinction of “megafauna” in the Americas 12,000 years ago — an extinction likely brought about by humans — altered the atmosphere’s methane concentrations, and thus the climate.

Summary: In May of 2010, Felisa Smith, Scott Elliott, and S. Kathleen Lyons published a letter in Nature Geoscience where they made a provocative argument. About 13,400 years ago, based on archeological evidence, humans crossed over the land bridge from Asia to North America. At the time, North and South America were populated with large mammals such as mammoths and giant ground sloths, and the density of these large animals exceeded that found in modern Africa. Yet within two thousand years, the majority of these large mammals were extinct, most likely due to successful human hunting.

About 12,500 years ago, the earth entered a period known as the “Younger Dryas,” when the planet temporarily cooled, and according to ice core records, the amount of methane in the atmosphere, the second most important greenhouse gas after CO2, decreased. These authors argued that the large mammals produced methane just as cattle produce the greenhouse gas today — through digestion of plant material — and that by eliminating these animals, humans had a noticeable effect on the concentration of methane in the atmosphere. 
Now a pair of scientists from Oregon State University are contesting this study. In a recent letter to Nature Geoscience, the scientists argue that the drop in atmospheric methane, which most researchers had previously assumed was due to wetland loss, wasn’t as unique as the original study suggested. The scientists also argued that the decrease in methane concentration was too small to significantly alter the climate.
The original authors then replied to this letter, defending their original calculation that a significant portion of the decrease in methane was due to these extinctions, and that the decrease was in fact unique when compared to earlier decreases. They concede that the effects on climate change cannot be readily predicted from the data, but argue that the “human-mediated extinction undoubtedly resulted in measureable impacts on biogeochemical cycles at the end of the last glacial period.”
This exchange highlights how science works: scientists challenging each other’s claims, based on different interpretations of scientific evidence.

Paper Title: Long-Term Climate Forcing in Loggerhead Sea Turtle Nesting

Journal: PLoS ONE

Authors: Kyle S. Van Houtan, John M. Halley

The Gist: Climate change may increase populations of Loggerhead turtles in the Atlantic Ocean, but decrease them in the Pacific.

Summary: This study models the effect of climate change on Loggerhead turtles, which are two to three foot long sea turtles that inhabit all of the world’s oceans except the Arctic. Loggerhead females only nest during years in which sea surface temperatures are within a particular range during the three months prior to egg-laying.


Climate also affects the percentage of hatchlings that survive to adulthood, and pervious studies have shown that more young turtles survive when the Pacific Decadal Oscillation, a climate cycle in the Pacific Ocean, is in its positive or “warm phase.” The authors assume that the situation is similar in the Atlantic, with more young turtles surviving when a climate cycle there is in its positive phase.


The study models how climate change may affect loggerhead populations, finding that over the next few decades, populations will increase for turtles that hatch in Florida, but decrease for those that hatch in Japan.

Paper: Environmental and economic effects of the Copenhagen pledges and more ambitious emission reduction targets
Journal: Energy Policy
Authors: Everett B. Peterson, Joachim Schleich, Vicki Duscha

Credit: Erland Howden/Flickr

The Gist: Countries could adopt much more aggressive plans to reduce emissions without significantly harming their economies or welfare.

Summary: Although the Copenhagen Accord, agreed upon in 2009, was not legally binding, most wealthy countries and many developing countries made specific pledges to reduce their greenhouse gas emissions. Nonetheless, the goals were modest, and even if these targets are met, total global pollution will increase (not decrease) by at least 10 percent in this decade.
The authors of this paper use a global economic model to estimate the economic consequences of implementing these targets, as well as the effects of implementing more aggressive ones. The more aggressive targets would be for wealthy countries to reduce their emissions by 30 percent in comparison to 1990 levels, and for select developing nations (such as China, India, and Brazil) to reduce their emissions by 15 percent in comparison to their expected growth.

The authors of this paper find that the economic effects are small for both the current policy and the more aggressive one: Global GDP is reduced by 0.2 to 0.3 percent for the current policy, and by about 0.5 percent for the more aggressive one. The burden, though, is not shared equally. Developing countries with targets would have their GDPs reduced by about 2.0 percent as compared to the expected levels, largely because their economic growth is more dependent on fossil fuels than wealthier nations.

Commentary: Beyond ocean acidification

Journal: Nature Geoscience

Author: Philip W. Boyd

The Gist: Ocean acidification is just one of the many stresses on marine life, and we need better research to understand how these various stresses interact.

Summary: Over the past two centuries, about half of the carbon dioxide that humanity has put into the atmosphere has been absorbed by the oceans, and because CO2 combines with water to create carbonic acid, the oceans have become more acidic by about 0.1 pH. In the next hundred years, due to rising CO2 concentrations, ocean pH could decline by another 0.5 pH, decreasing at a rate that is, as the author says, “unprecedented in the past 300 million years.”

More acidic oceans may harm marine creatures that make hard shells out of calcium carbonate, such as corals, and disrupt chemical processes in many species. Over the past decade, research has focused on the direct consequences of ocean acidification. The author of this commentary argues that the next decade of research must focus on how ocean acidification will interact with other stressors on the marine environment. These stressors include rising temperatures, changes in river runoff, increased stratification of the ocean (brought about by warmer waters), and rising sea levels that alter coastal ecosystems. Little is known about how these factors, in combination, will affect marine ecosystems.

Paper Title: Climate change, sea level rise and rice: global market implications

Journal: Climatic Change

Authors: Chi-Chung Chen, Bruce McCar, and Ching-Cheng Chang

The Gist: Climate change will negatively affect rice production because rising sea levels will flood agricultural land and warmer temperatures will reduce rice yields.

Summary: Using previous studies that estimate the effects of climate change on rice yields, and drawing on estimates of the amount of agricultural land vulnerable to sea level rise, the authors of this paper build an economic model to determine the effects of climate change on the global rice market in 2030 and 2080.

The model shows that the countries whose rice yields are most affected by warmer temperatures will be Indonesia, Korea, the Philippines, Brazil, India, and Pakistan. The countries whose crops will be most impacted by sea level rise are Bangladesh, Japan, Taiwan, Myanmar, Vietnam, and Egypt. Due to sea level rise alone, Myanmar, Vietnam, and Egypt may change from being net exporters to net importers of rice. In all, the authors estimate that climate change will increase global rice prices by 17 to 21 percent by 2030.

Paper Title: A rose by any other name…?: What members of the general public prefer to call “climate change”

Journal: Climatic Change

Authors: Karen Akerlof and Edward W. Maibach

The Gist: While most people don’t have a strong preference between the phrases “climate change,” “global warming,” and “global climate change,” people who believe climate change is a serious issue are more likely to use the phrase “global warming.”

Summary: Via a mail-in form, researchers surveyed over 700 adults to determine how people think about and use the phrases “global warming,” “climate change,” and “global climate change.” About 40 percent of respondents said that they had no preference between the terms.

People who said that global warming is caused by humans were six times more likely to prefer the phrase “global warming” than those who said climate change was mostly naturally caused, and 17 times more likely to prefer the phrase “global warming” than people who don’t believe the planet is warming at all.

In general, the more concerned someone was with the issue, the more likely they were to use and prefer “global warming.” The authors suggest that the phrase “climate change” may be less politically divisive.

Paper Title: Shifts in biogenic carbon flow from particulate to dissolved forms under high carbon dioxide and warm ocean conditions

Journal: Geophysical Research Letters

Authors: Ja‐Myung Kim, Kitack Lee, Kyungsoon Shin, Eun Jin Yang, Anja Engel, David M. Karl, and Hyun‐Cheol Kim

The Gist: Climate change may weaken the ocean’s “biological carbon pump,” which would slow the ability of the ocean to remove CO2 from the atmosphere.

Summary: The ocean’s “biological carbon pump” is a natural process by which the ocean removes carbon from surface waters and deposits it at the ocean floor. Phytoplankton consume CO2 near the surface, turning it into biomass and fueling the food chain. Some of the ecosystem’s biomass ends up sinking to the ocean floor, removing carbon from the surface waters and allowing more CO2 to be absorbed from the atmosphere. If this natural pump were to slow down, it would mean that CO2 would build up more quickly in the atmosphere, thus accelerating climate change.
The authors of this study used large transparent tanks in coastal waters off South Korea and artificially raised the CO2 levels to 900 parts per million, and warmed the tanks by about 3°C — a probable future for the end of this century. They then measured the particulate organic carbon in the tanks.

They found that the ratio of particulate carbon to dissolved carbon was less for the warmer tank. If the entire ocean responds similarly, then the biological carbon pump will be lessened, thus accelerating climate change. The authors admit, though, that these findings are preliminary, and they hesitated to extrapolate their findings to the entire ocean.