Climate Change and Environment


"New Politics for Clean Energy," Project Syndicate, April 27, 2016 

"The big difference between Clinton and Sanders," CNN, March 9, 2016 


"Jeffrey D. Sachs on How to Forge a Grand Bargain on Energy," The Wall Street Journal, December 31, 2015

"From Good Intentions to Deep Decarbonization," with Guido Schmidt-Traub and Jim Williams, Project Syndicate, December 4, 2015

 "The Clean-Energy Moonshot," Project Syndicate, October 6, 2015 

 "The Data Revolution for Sustainable Development," Shaida Badiee, Robert Chen and Enrico Giovannini, Project Syndicate, September 18, 2015 

"The G-7 Embraces Decarbonization," Project Syndicate, June 10, 2015

"Climate Change and the Catholic Church," Project Syndicate, May 3, 2015.

"ExxonMobil’s Dangerous Business Strategy," Project Syndicate, April 17, 2015.

"Why the Sustainable Development Goals Matter," Project Syndicate, March 30, 2015.

"By separating nature from economics, we have walked blindly into tragedy," The Guardian, March 10, 2015.

"No Hiding From Sustainable Development," Project Syndicate, March 3, 2015.

"The real climate battle after a sweltering 2014," Financial Times, January 18, 2015.


"The Year of Sustainable Development," Project Syndicate, December 9, 2014.

"The climate breakthrough in Beijing gives the world a fighting chance," Financial Times, November 12, 2014. Download [PDF here]


"Sustainable Development Goals for a New Era," HORIZONS, September 22, 2014. Download [PDF here]

"The 'Wall Street Journal' Parade of Climate Lies," Huffington Post, September 6, 2014. [PDF here]

"The G20, human health and sustainability: an interview with Jeffrey D Sachs," Medical Journal of Australia, August 2014. Download [PDF here]

"How to decarbonise the global economy," Financial Times, July 8, 2014. [Download PDF here]

"The Limits of Climate Negotiations," Project Syndicate, June 23, 2014. Download as [PDF]

"The EPA Is Right and US Chamber of Commerce Is Wrong on Climate Change," Huffington Post, June 16, 2014. Download as [PDF]

"Interview with UNCCD News," UNCCD News, June 9, 2014. Download as [PDF]

"Kudos to the White House and EPA on the New Climate Regulations," Huffington Post, June 3, 2014. Download as [PDF]

"Our Last Chance for a Safe Planet," Project Syndicate, May 28, 2014. Download as [PDF]

"How the AEI Distorts the Climate Debate," Huffington Post, February 8, 2014. Download as [PDF]

"Keystone: The Pipeline to Disaster," Huffington Post, February 3, 2014. Download as [PDF]

"Europe still sets the standard for a low-carbon future", Financial Times, January 28, 2014. Download [PDF here]

"The challenge of deep decarbonisation," The Gulf News, January 22, 2014. Download as [PDF]

"The Case for Aid," Foreign Policy, January 21, 2014. Download as [PDF]


"The Age of Sustainable Development," Project Syndicate, December 23, 2013. Download as [PDF]

"Cities and Sustainable Development," Project Syndicate, November 25, 2013. Download as [PDF]

"A few more storms like Typhoon Haiyan may finally make our leaders act on climate change," Washington Post, November 15, 2013. Download as [PDF]

"We risk more Haiyans if we ignore climate change," Financial Times, November 15, 2013. [Download as PDF]

"The End of Poverty, Soon," New York Times, September 25, 2013. Download as [PDF]

"High stakes at the UN on the Sustainable Development Goals," The Lancet, September 19, 2013. Download as [PDF]

"New United Nations initiative on sustainable development comes to campus," Columbia Spectator, September 17, 2013. Download as [PDF]

"Global Development’s Winning Goals," Project Syndicate, August 27, 2013. Download as [PDF]

"A General Equilibrium Model for Analyzing African Rural Subsistence Economies and an African Green Revolution," with John W. McArthur, Brookings Africa Growth Initiative Working Paper 12, June 2013. Download as [PDF]

"Q&A: Jeffrey Sachs on the world's post-MDG future," SciDev.Net, June 12, 2013. Download as [PDF]

"Sustainable Visions," Project Syndicate, June 7, 2013. Download as [PDF]

"Paths to Sustainable Power," Project Syndicate, March 28, 2013. Download as [PDF]

"A Better Way to Fight Climate Change," Project Syndicate, February 28, 2013. Download as [PDF]

"America’s New Progressive Era?" Project Syndicate, January 31, 2013. Download as [PDF]

"Writing the Future," Project Syndicate, January 24, 2013. Download as [PDF]


 "Polluters Must Pay," Project Syndicate, November 26, 2012. Download as [PDF]

"Obama Has Four Years to Fix the Economy," Financial Times, November 11, 2012. [Download as PDF]

"Attention, Mr. President: No Politics, Just Our Solutions — Saving the Climate," Parade, November 4, 2012. Download as [PDF]

"A Global Solutions Network," Project Syndicate, August 22, 2012. Download as [PDF]

"Green Growth and Equity in the Context of Climate Change: Some Considerations," with Shiv Someshwar. ADBI Working Paper Series 371, July 2012. Download as [PDF]

"Our Summer of Climate Truth," Project Syndicate, July 27, 2012. Download as [PDF]

"A Rio Report Card," Project Syndicate, June 18, 2012. Download as [PDF]

"From Millennium Development Goals to Sustainable Development Goals," The Lancet, June 9, 2012. Download as [PDF]

"The future of development goals," in the Commonwealth Ministers Reference Book 2012[Download as PDF]

"A World Adrift," Project Syndicate, 22 April 2012. [Download as PDF]

"Sustainable Humanity," Project Syndicate, January 31, 2012. [Download as PDF]


"Effective monitoring of agriculture: a response," Journal of Environmental Monitoring, December 20, 2011. [Download as PDF]

"What sort of world awaits the seven billionth person?" Irish Times, October 28, 2011. [Download as PDF]

"The Murdoch Legacy," Huffington Post, October 10, 2011. [Download as PDF]

"In the Front Line," Our Planet, September 2011. [Download as PDF]

"Famine and Hope in the Horn of Africa." Project Syndicate. July 31, 2011. [Download as PDF]

"Ban Ki-moon and the Age of Sustainable Development," Project Syndicate, June 24, 2011. [Download as PDF]

"Need Versus Greed," Project Syndicate, February 28, 2011. [Download as PDF]


"Fighting for Survival: Sustainability in the Gulf" with Irwin Redlener, M.D. The Huffington Post. November 1, 2010. [Download as PDF]

"A New Path to a Low-Carbon Economy," Project Syndicate, October 27, 2010. [Download as PDF]

"Growth in a Buddhist Economy," Project Syndicate, August 25, 2010. [Download as PDF]

"Making Sense of the Climate Impasse," Huffington Post, August 2, 2010. [Download as PDF]

"Monitoring the world's agriculture," with Roseline Remans et al., Nature, July 29, 2010. [Download as PDF]


"Hold the rich nations to their word," Financial Times, 16 December 2009. [Download as PDF]

"End the Politics -- Let Scientists and Engineers Lead," Huffington Post, 3 December 2009. [Download as PDF]

"Enough posturing politics. Time to let the experts lead." The Guardian. 2 December 2009. [Download as PDF]

"Transgressing Planetary Boundaries," Scientific American, December 2009. [Download as PDF]

"A Clunker of a Climate Policy." Scientific American. November 2009. [Download as PDF]

"It's too late to seal a global climate deal. But we need action, not Kyoto II." The Guardian. 30 September 2009.

"Biodivesity Conservation and the Millennium Development Goals." with Jonathan E. M. Baillie, William J. Sutherland, Paul R. Armsworth, Neville Ash, John Beddington, Tim M. Blackburn, Ben Collen, Barry Gardiner, Kevin J. Gaston, H. Charles J. Godfray, Rhys E. Green, Paul H. Harvey, Brett House, Sandra Knapp, Noëlle F. Kümpel, David W. Macdonald, Georgina M. Mace, James Mallet, Adam Matthews, Robert M. May, Owen Petchey, Andy Purvis, Dilys Roe, Kamran Safi , Kerry Turner, Matt Walpole, Robert Watson, Kate E. Jones. Science. 18 September 2009. [Download as PDF]

"Digital Soil Map of the World." with Pedro A. Sanchez, Sonya Ahamed, Florence Carré, Alfred E. Hartemink, Jonathan Hempel, Jeroen Huising, Philippe Lagacherie, Alex B. McBratney, Neil J. McKenzie, Maria de Lourdes Mendonça-Santos, Budiman Minasny, Luca Montanarella, Peter Okoth, Cheryl A. Palm, Keith D. Shepherd, Tor-Gunnar Vågen, Bernard Vanlauwe, Markus G. Walsh, Leigh A. Winowiecki, Gan-Lin Zhang. Science. 7 August 2009.

"Still Needed: A Climate Plan." Scientific American. July 2009.

"Putting a Price on Carbon: An Emissions Cap or a Tax?" Yale Environment 360. 7 May 2009. [Download as PDF]

"Transforming the Auto Industry." Scientific American. February 2009. [Download as PDF]

"An Industrial Policy for Climate Change." McKinsey Quarterly. 23 February 2009. [Download as PDF]

"Eight Principles for a Global Agreement on Climate Change." COP15 UN Climate Change Change Conference Blog. 28 January 2009. [Download as PDF]


Common Wealth: Economics for a Crowded Planet, Penguin Press, 2008.

"Looking after the Future." Scientific American. November 2008.

"Better Cities, Better Life: Challenges for Shanghai." Shanghai Daily. 12 November 2008. [Download as PDF]

"Coping with a Persistent Oil Crisis." Scientific American. October 2008.

"Amid the rubble of global finance, a blueprint for Bretton Woods II." The Guardian. 21 October 2008. [Download as PDF]

"The Specter of Malthus Returns." Scientific American. September 2008.

"Using Carbon Taxes to Pay for Development." Financial Times. 24 September 2008. [Download as PDF]

"Land, Water and Conflict." Newsweek. July 2008. [Download as PDF]

"Climate Change: feed it and weep, or lead and reap." Sydney Morning Herald. 25 July 2008. [Download as PDF]

"A User's Guide to the Century." The National Interest. 2 July 2008. [Download as PDF]

"Less talk, more action needed." The Guardian. 25 June 2008.

"Stagflation is Back. Here's How to Beat It." Fortune. 9 June 2008.

"We Need a Power Surge." Time Magazine. 29 May 2008. [Download as PDF]

"Technological Keys to Climate Protection." Scientific American. March 2008. [Download as PDF]

Slate Book Club on Common Wealth: Economics for a Crowded Planet. [Download as PDF]

"Common Wealth." TIME Magazine. March 2008. [Download as PDF]

Bien Común.”  Centro de Investigación Social, Un Techo Para Chile.  Año 7, No. 12.  Segundo Semestre 2008.  Santiago, Chile, translated from “Common Wealth” TIME Magazine, March 2008.

"Climate Change after Bali." Scientific American. February 2008. [Download as PDF]


"Meaningful Goals for Climate Talks." Scientific American. December 2007. [Download as PDF]

"Climate Change and the Law." Scientific American. November 2007. [Download as PDF]

The African Millennium Villages,” with Pedro Sanchez, Cheryl Palm, Glenn Denning, Rafael Flor, Rebbie Harawa, Bashir Jama, Tsegazeab Kiflemariam, Bronwen Konecky, Raffaela Kozar, Eliud Lelerai, Alia Malik, Vijay Modi, Patrick Mutuo, Amadou Niang, Herine Okoth, Frank Place, Sonia Ehrlich Sachs, Amir Said, David Siriri, Awash Teklehaimanot, Karen Wang, Justine Wangila, and Colleen Zamba. Proceedings of the National Academy of Sciences Special Feature: Sustainability Science, 104 , no. 43 (October, 23 2007): 1677580.

"Making Development Less Risky." Scientific American. August 2007. [Download as PDF]

"The Promise of the Blue Revolution." Scientific American. July 2007.
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"The Secretary-General: Indispensable for Sustainable Development." UN Chronicle. Issue 1, 2007.
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"Climate Change Refugees." Scientific American. June 2007.
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"How I'd fix the World Bank." Fortune. 26 June 2007.
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"The Road to Clean Energy Starts Here." Scientific American. May 2007.
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"A Climate For Change." TIME Magazine. 8 March 2007.

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"Moving Beyond Kyoto." Scientifc American. February 2007.
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"The Challenge of Sustainable Water." Scientific American. December 2006.
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"Fiddling While the Planet Burns." Scientific American. October 2006.
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"Does Conservation Matter to the Poor?" Nature Conservancy Magazine. Summer 2006. 
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"Ecology and Political Upheaval." Scientific American. July 2006.
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"Pay for it Now, or Pay for it Later." The Globe and Mail. 19 June 2006.
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"The New Geopolitics." Scientific American. June 2006.
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"Investments Toward Sustainable Development," with Walter V. Reid. Science, Vol. 312. 19 May 2006.
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"A Robust Strategy for Sustainable Energy," with Klaus Lackner. Brookings Papers on Economic Activity, Issue 2. 2005.
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2005 U.N. World Summit Blog, Financial Times (online),  September 12-16, 2005.
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"What the President Doesn't Want to Hear," Esquire, February 2005.
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"The Class System of Catastrophe," Time, January 10, 2005.
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“We Can End World Hunger: Here’s How,” with Pedro Sanchez, World Ark, November/ December 2004.
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"Mother of All Headaches," Review of The End of Oil and Energy at the CrossroadsOnEarth Magazine, Summer 2004.
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"Seeking a Global Solution: The Copenhagen Consensus neglects the need to tackle climate change," Nature, August 12, 2004.
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"Une révolution verte pour l'Afrique," with Pedro Sanchez, Le Monde, August 10, 2004.
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"Sustainable Development," Science, April 30 2004.
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"Getting Through the Bottleneck," Our Planet: The Magazine of the UNEP, Vol. 13 No 4. (2003 Issue: Globalization, Poverty, Trade, and the Environment)  [Download as PDF]

"The Strategic Significance of Global Inequality," (reprint) Environmental Change and Security Project Report, Woodrow Wilson International Center for Scholars, Issue 9, 2003.
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"America's disastrous energy plan,"Financial Times, December 23, 2003
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"Institutions Don't Rule: Direct Effects of Geography on Per Capita Income," NBER Working Paper 9490, January 2003.
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[Download Stata data file]
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(Note: results differ slightly from NBER version due to updated malaria data)


"Compensation for 'Meaningful Participation' in Climate Change Control: A Modest Proposal and Empirical Analysis" with T. Panayotou and A. Peterson Zwane, Journal of Environmental Economics and Management,  43, pp. 437-454, 2002.
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"The Essential Ingredient," New Scientist, August 17, 2002. [Download as PDF]

"How to save the world in Johannesburg," Financial Times, August 13, 2002
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"Reducing the Vulnerability to Natural Disasters: Hurricane Mitch and Central America," with Juan Carlos Barahona, Eduardo Doryan and Felipe B. Larrain Economic Development in Central America, Vol. II: Structural Reform edited by Felipe B. Larrain.  Harvard University Press, 2001.
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"Is the Environmental Kuznets Curve Driven by Structural Change? What Extended Time Series May Imply for Developing Countries" with Theo Panayotou and Alix Peterson. CAER II No. 80, 2000.
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"Climate, Coastal Proximity, and Development," with Andrew Mellinger and John Gallup in Oxford Handbook of Economic Geography, edited by Gordon L. Clark, Maryann P. Feldman, and Meric S. Gertler, Oxford University Press, 2000.
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(Previously "Climate, Water Navigability, and Economic Development," with Andrew Mellinger and John Gallup, CID Working Paper No. 24, September 1999. [PDF])

"Natural Resource Abundance and Economic Growth," with Andrew Warner, Leading Issues in Economic Development, Oxford University Press, 2000.
Reprinted in Spanish as "Recursos Naturales y Desarollo Economico" in Mineria y Desarollo, Gustavo Lagos (ed.), Foro en Economia de Minerales, Vol. 3, 2005.
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[Download Stata data file]
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"Agriculture, Climate, and Technology: Why are the Tropics Falling Behind?" with John Luke Gallup, American Journal of Agricultural Economics.  Vol. 82, pp. 731-777, August 2000.
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"Developing Countries and the Control of Climate Change: A Theoretical Perspective and Policy Implications," with Theodore Panayotou and Alix Peterson. HIID CAER II Discussion Paper No. 44, November 1999. [Download as PDF]

"Developing Countries and the Control of Climate Change: Empirical Evidence" with Theo Panayotou and Alix Peterson, CAER II Discussion Paper No. 45, August 1999. CC [Download paper as PDF]

"Developing Countries and the Control of Climate Change: A Theoretical Perspective and Policy Implications," with Theo Panayotou and Alix Peterson, prepared for UNAID/CAER II, CAER II Discussion Paper No. 44, August 1999. [Download paper as PDF]


Susan Solomon

Solomon led efforts to identify the cause of the ozone hole over Antarctica

An American atmospheric chemist who led efforts to identify the cause of the Antarctic ozone hole and a French geochemist who extracted the longest-yet climate record from polar ice cores have won the prestigious 2012 Vetlesen Prize. Susan Solomon and Jean Jouzel will share the $250,000 award, considered to be the earth sciences’ equivalent of a Nobel.

“Earth Science is a collective enterprise, and transformational advances are the product of many authors,” says the Vetlesen Prize committee’s citation. “Both nominees have made leading and fundamental contributions to climate science.” The prize is funded by the G. Unger Vetlesen Foundation in New York and administered by Columbia University’s Lamont-Doherty Earth Observatory.

Solomon’s work in identifying the cause of Antarctica’s springtime ozone losses helped bring about a global ban on manmade ozone-depleting chemicals. Working most of her career at the National Oceanic and Atmospheric Administration (NOAA) in Boulder, Colo., Solomon proposed in a 1986 study  that refrigerants and other industrial chemicals were responsible for the Antarctic ozone hole discovered a year earlier. She led two expeditions to Antarctica, in 1986 and 1987, bringing back key measurements that proved her hypothesis. Recognizing that ozone protects the planet from harmful ultraviolet rays that can cause skin cancer, policymakers around the world responded with rare speed: in 1987, they agreed on a Montreal Protocol to phase out the use of chlorofluorocarbons (CFCs) and related chemicals.

Solomon and her colleagues also explained why ozone destruction was greatest during southern spring. Throughout the dark and extremely cold winter, CFC byproducts react with icy stratospheric clouds to produce ozone-depleting chlorine compounds. When sunlight returns to the South Pole, it reacts with the compounds to break ozone apart.  In a 2002 study, Solomon and a colleague also linked Antarctica’s ozone hole to a strengthening of winds that circle the continent in summer, causing net cooling over most of Antarctica but extreme warming over the West Antarctic Peninsula.  She has also written several books. In The Coldest March, published in 2002, she reconstructed the weather during British explorer Robert Scott’s 1911 expedition to Antarctica to argue that abnormally cold conditions and not incompetence led to the deaths of Scott and his crew. She has also worked as a member of the Intergovernmental Panel on Climate Change (IPCC), which in 2007 received the Nobel Peace Prize.  Solomon, 56, is the first woman to win the Vetlesen since it was first offered in 1960.

Jouzel, 65, has been involved in collecting ice-core records from both poles since the 1970s, and has advanced isotopic techniques for extracting past climate information from them. In the longest climate reconstruction yet from ice cores, Jouzel in a 2007 study in the journal Science charted temperatures in Antarctica for the last 800,000 years, over eight consecutive ice ages. The record was long enough to highlight Antarctica’s climate response to slowly varying seasonal distribution of sunlight caused by changes in earth’s orbit. It was also detailed enough to reveal climate variations within each ice age cycle due to earth’s complex internal climate system.

He has also been a leader in bringing human-caused climate change to the public’s attention.

Jean Jouzel

Jouzel has collected the longest-yet climate record from polar ice cores.

For the last 20 years, he has worked on the IPCC, and is currently vice president of the climate science working panel, whose findings will be released in the Fifth Assessment Report next September.  Jouzel has co-written several books, including Climate: A Dangerous Game in 2007 and White Planet, whose English translation is due out in 2013.

Neither scientist came from a scientific family. Solomon was born and raised in Chicago; her father sold insurance and her mother taught fourth grade. She says she was inspired to become a scientist by watching oceanographer Jacques Cousteau on TV as a child, and to go into chemistry by the “exactness” of the experiments she did in high school. “You have a clear solution and you add an exact amount of base and wow, it changes to a bright color just like it’s supposed to,” she said. She received her Ph.D. from the University of California at Berkeley in 1981, and worked at NOAA until 2011, when she became a professor at the Massachusetts Institute of Technology. She has won many previous honors: the American Geophysical Union (AGU)’s Macelewane Medal in 1985 for early-career achievement; a U.S. National Medal of Science in 1999, and the Blue Planet Prize in 2004.

Jouzel grew up in a farming family in Brittany, and during his graduate studies in chemistry became interested in how large hailstones form in the atmosphere at a time when chemical seeding of clouds to produce rain was a popular research topic. He received his Ph.D. in chemistry from the Faculté d’Orsay in Paris in 1974 and eventually applied his hail-investigation techniques to polar ice cores, advancing methods for pulling climate information from air bubbles trapped in the ice and minute variations in water molecules layered in the cores.

He has spent his research career at the French nuclear agency, CEA, or Commissariat à l'Energie Atomique. In 1995, he became research director of CEA’s climate and environment lab (LSCE), and from 2001 to 2008, headed the Institut Pierre-Simon Laplace, a national climate research lab near Paris that includes LSCE. In 2002, Jouzel and his mentor Claude Lorius received France’s highest scientific honor, the CNRS gold medal, for their work on polar ice cores, including reconstruction of past greenhouse gas levels from air trapped in the ice. In 1997, he was awarded the European Geophysical Society’s Milankovitch Medal for outstanding research on long-term climate change and modeling; and in 2003, AGU’s Roger Revelle medal for outstanding contributions to atmospheric science.

“If we want to avoid large climate change we need to act now on greenhouse gases,” he said. “Global warming is not yet damaging, but if we do nothing in the coming years we will have more extreme events, droughts, storms and so on.”

The Vetlesen Prize is given “for scientific achievement resulting in a clearer understanding of the Earth, its history, or its relations to the universe.” It was established in 1959 by the trustees of the estate of G. Unger Vetlesen, a Norwegian immigrant to the United States who became a leading shipbuilder, World War II military leader and pioneer in transatlantic air travel. Vetlesen passed away in 1955. Designed to recognize sweeping achievements on par with the Nobel, it is given every several years by a selection committee appointed by the president of Columbia University. The most recent award was in 2008 to maverick geologist Walter Alvarez, who convinced the world that an asteroid strike wiped out the dinosaurs. Previous winners include British climate scientist Sir Nicholas Shackleton, and several scientists at Lamont-Doherty itself, including climate scientist Wallace Broecker, marine geologist Walter Pitman, seismologist Lynn Sykes and Lamont’s founding director Maurice “Doc” Ewing.

Solomon and Jouzel will receive the award and accompanying medal from Columbia president Lee Bollinger at the university’s Low Library on Feb. 21.

A video interview with Susan Solomon
Jean Jouzel Biography

The deep-sea benthic foram Aragonia  velascoensis went extinct about 56 million years ago as the oceans rapidly acidified.

The deep-sea benthic foram Aragonia velascoensis went extinct about 56 million years ago as the oceans rapidly acidified. (Ellen Thomas/Yale University)

Some 56 million years ago, a massive pulse of carbon dioxide into the atmosphere sent global temperatures soaring. In the oceans, carbonate sediments dissolved, some organisms went extinct and others evolved.

Scientists have long suspected that ocean acidification played a part in the crisis—similar to today, as manmade CO2 combines with seawater to change its chemistry. Now, for the first time, scientists have quantified the extent of surface acidification from those ancient days, and the news is not good: the oceans are on track to acidify at least as much as they did then, only at a much faster rate.  

In a study published in the latest issue of Paleoceanography, the scientists estimate that surface ocean acidity increased by about 100 percent in a few thousand years or more, and stayed that way for the next 70,000 years. In this radically changed environment, some creatures died out while others adapted and evolved. The study is the first to use the chemical composition of fossils to reconstruct surface ocean acidity at the Paleocene-Eocene Thermal Maximum (PETM), a period of intense warming on land and throughout the oceans due to high CO2.

“This could be the closest geological analog to modern ocean acidification,” said study coauthor Bärbel Hönisch, a paleoceanographer at Columbia University’s Lamont-Doherty Earth Observatory. “As massive as it was, it still happened about 10 times more slowly than what we are doing today.”

The oceans have absorbed about a third of the carbon humans have pumped into the air since industrialization, helping to keep temperatures lower than they would be otherwise. But that uptake of carbon has come at a price. Chemical reactions caused by that excess CO2 have made seawater grow more acidic, depleting it of the carbonate ions that corals, mollusks and calcifying plankton need to build their shells and skeletons.

In the last 150 years or so, the pH of the oceans has dropped substantially, from 8.2 to 8.1--equivalent to a 25 percent increase in acidity. By the end of the century, ocean pH is projected to fall another 0.3 pH units, to 7.8. While the researchers found a comparable pH drop during the PETM--0.3 units--the shift happened over a few thousand years.

“We are dumping carbon in the atmosphere and ocean at a much higher rate today—within centuries,” said study coauthor Richard Zeebe, a paleoceanographer at the University of Hawaii. “If we continue on the emissions path we are on right now, acidification of the surface ocean will be way more dramatic than during the PETM.”

Ocean acidification in the modern ocean may already be affecting some marine life, as shown by the partly dissolved shell of this planktic snail, or pteropod, caught off the Pacific Northwest.

Ocean acidification in the modern ocean is already affecting some marine life, as shown by the partly dissolved shell of this planktic snail, or pteropod, caught off the Pacific Northwest. (Nina Bednaršek/NOAA)

The study confirms that the acidified conditions lasted for 70,000 years or more, consistent with previous model-based estimates. “It didn’t bounce back right away,” said Timothy Bralower, a researcher at Penn State who was not involved in the study. “It took tens of thousands of years to recover.”

From seafloor sediments drilled off Japan, the researchers analyzed the shells of plankton that lived at the surface of the ocean during the PETM. Two different methods for measuring ocean chemistry at the time—the ratio of boron isotopes in their shells, and the amount of boron --arrived at similar estimates of acidification. “It’s really showing us clear evidence of a change in pH for the first time,” said Bralower.

What caused the burst of carbon at the PETM is still unclear. One popular explanation is that an overall warming trend may have sent a pulse of methane from the seafloor into the air, setting off events that released more earth-warming gases into the air and oceans. Up to half of the tiny animals that live in mud on the seafloor—benthic foraminifera—died out during the PETM, possibly along with life further up the food chain.  

Other species thrived in this changed environment and new ones evolved.  In the oceans, dinoflagellates extended their range from the tropics to the Arctic, while on land, hoofed animals and primates appeared for the first time. Eventually, the oceans and atmosphere recovered as elements from eroded rocks washed into the sea and neutralized the acid.

Today, signs are already emerging that some marine life may be in trouble. In a recent study led by Nina Bednaršek at the U.S. National Oceanic and Atmospheric Administration, more than half of the tiny planktic snails, or pteropods, that she and her team studied off the coast of Washington, Oregon and California showed badly dissolved shells. Ocean acidification has been linked to the widespread death of baby oysters off Washington and Oregon since 2005, and may also pose a threat to coral reefs, which are under additional pressure from pollution and warming ocean temperatures.  

“Seawater carbonate chemistry is complex but the mechanism underlying ocean acidification is very simple,” said study lead author Donald Penman, a graduate student at University of California at Santa Cruz. “We can make accurate predictions about how carbonate chemistry will respond to increasing carbon dioxide levels. The real unknown is how individual organisms will respond and how that cascades through ecosystems.”

Other authors of the study, which was funded by the U.S. National Science Foundation: Ellen Thomas, Yale University; and James Zachos, UC Santa Cruz.

Bärbel Hönisch Lecture on Ocean Acidification
Ocean Acidification Rate May Be Unprecedented, Study Says

A new study projects that much of Ethiopia, Somalia and Djibouti in the Horn of Africa will grow drier as global warming progresses. Here in northern Ethiopia, herders often already struggle to make a living.

A new study projects that much of Ethiopia, Somalia and Djibouti in the Horn of Africa will grow drier as global warming progresses. Here in northern Ethiopia, herders often already struggle to make a living. (Brian Kahn/IRI)

A new study finds that the Horn of Africa has become progressively drier over the past century and that it is drying at a rate that is both unusual in the context of the past 2,000 years and in step with human-influenced warming. The study also projects that the drying will continue as the region gets warmer. If the researchers are right, the trend could exacerbate tensions in one of the most unstable regions in the world.

“Right now, aid groups are expecting a wetter, greener future for the Horn of Africa, but our findings show that the exact opposite is occurring. The region is drying and will continue to do so with rising carbon emissions,” said study coauthor Peter deMenocal, who heads the Center for Climate and Life at Columbia University’s Lamont-Doherty Earth Observatory.

The study, appearing in this week’s Science Advances, used a sediment core that deMenocal and his colleagues extracted from the pirate-ridden Gulf of Aden. They used the core to infer past changes in temperature and aridity. By pairing the paleoclimate record from the core with 20th century observations, the researchers determined that drying will probably continue across Somalia, Djibouti and Ethiopia. That contradicts more optimistic models that have suggested future warming might bring rainier weather patterns that could benefit the region.

“What we see in the paleoclimate record from the last 2,000 years is evidence that the Horn of Africa is drier when there are warm conditions on Earth, and wetter when it is colder,” said lead author Jessica Tierney, an associate professor at the University of Arizona and former postdoctoral associate at Lamont-Doherty. 

Global-scale models used to predict future changes under global warming suggest that the region should become wetter, primarily during the “short rains” season from September to November. But the new study suggests that those gains may be offset by declining rainfall during the “long rains” season from March to May, on which the region’s rain-fed agriculture relies.

Study coauthor Peter deMenocal (left) took this deep-sea core in the pirate-infested Gulf of Aden. Lead author Jessica Tierney (right) performed an analysis linking greater heat in the past to drier conditions.

Study coauthor Peter deMenocal (left) took this deep-sea core in the pirate-infested Gulf of Aden. Lead author Jessica Tierney (right) performed an analysis linking greater heat in the past to drier conditions. (Courtesy Lamont-Doherty Earth Observatory)

The outcome has serious implications for a region that has been racked with political instability and violence as it has dried. The Horn of Africa has suffered deadly droughts every few years in recent decades, and with them humanitarian crises as famine and violence spread. It has also become one of the most unstable regions in the world. In Somalia, as the political situation deteriorated amid droughts of the 1980s and `90s, hundreds of thousands of refugees fled the country, and pirates began raiding ships off the coast.

To extract the sediment core used in the study, scientists had to evade those pirates in the Gulf of Aden. Lamont-Doherty’s R/V Maurice Ewing had been attacked with rocket-propelled grenades during a previous trip.On this run, the captain of the Dutch research ship Pelagia turned off the ship’s interior and navigation lights to slip through these waters. Around them, other vessels were reporting pirate attacks.

That sediment core, which dates back about 40,000 years, has already provided new insights into Africa’s climate. In a 2013 study analyzing parts of the core, Tierney and deMenocal showed that the Sahara, which once bloomed with regular rainfall, suddenly dried out over the span of a century or two, during a warm period some 5,000 years ago—not more gradually, as many researchers had assumed. It provided evidence that climate shifts can happen quite suddenly, even if the forces driving them are gradual.

The new study uses isotopes from leaf waxes found in the sediment sample to compare rates of drying over the past 2,000 years. Plants reflect the environment that sustains them. When the climate is drier, leaf waxes are more enriched with deuterium, or heavy hydrogen isotopes; leaf waxes from wetter climates reflect the more abundant rainfall through the presence of the normal hydrogen isotopes. The researchers found an increasing shift toward heavy hydrogen in the last century as the climate, which had experienced a wet period during the Little Ice Age (1450—1850 AD), dried out.

The findings suggest that climate modeling, frequently done at a global scale, would benefit from region-specific studies with higher resolution results in high-impact areas such as the Horn of Africa, Tierney said.

“If we can simulate rainfall in these arid tropical and subtropical regions better, we can understand the future impact of climate change,” she said.

The study’s other coauthor is Caroline Ummenhofer of Woods Hole Oceanographic Institution.