Q: The average global temperature has dropped two degrees in the past two years. Crop yields are projected to decline 10 percent in 2009 due to cooler growing conditions. Approximately 85 percent of CO2 is not from man-made sources. Countries outside the United States produce the majority of CO2 and their growth rate is accelerating. If global warming is actually due to man, rather than sunspots or other natural causes, how can the current efforts to minimize CO2 emissions before we have replacement technology be cost justified?
Asked by Daniel Wildermuth, ’87, Alpharetta, Ga.
Just yesterday I wondered about this same topic. I was walking home to Escondido Village from a party around 2 a.m., and man was it cold! I found out this morning that the temperature the previous night had dipped to 37 degrees Fahrenheit—compared to 65 degrees the day before. That's a cooling of 28 degrees Fahrenheit—in just a few hours! And to top it all off, I had no crop yields at all the following morning.
Okay, maybe that's a little different. But your question taps into the debate that's been raging between climate scientists and climate skeptics over whether the world's climate is changing due to human causes. Scientists agree that human activity is increasing greenhouse gases such as carbon dioxide, which in turn trap more heat in the Earth's atmosphere—the so-called greenhouse effect. Skeptics, on the other hand, disagree that global warming is caused by humans, or that it is happening at all. The notion of "global cooling" fits in nicely with this "contrarian" storyline.
There have been a number of high-profile claims that world temperatures are dropping, including in the recent SuperFreakonomics. The authors of that book—an economist and a journalist—claim: "While the drumbeat of [climate change] has grown louder over the past several years, the average global temperature during that time has in fact decreased."
Temperatures are going up and down all the time, so a selective reading of the data can find almost any trend, which was what led the authors of SuperFreakonomics to claim the world is cooling. Co-author Steven Levitt said he "eye-balled" the numbers and noticed 2005 was hotter than the years after it, but he did not do any sort of statistical analysis to back up his blanket statement on global cooling. The authors have since retracted their global cooling antics, stating in their blog: "We believe that rising global temperatures are a man-made phenomenon and that global warming is an important issue to solve."
Unfortunately, various versions of this mistaken critique continue to circulate. The Associated Press recently commissioned an independent study, asking distinguished statisticians from around the world to examine a set of data and look for trends. They didn't tell the statisticians it was global temperature data. Not one expert reported a downward trend. Global cooling, it seems, is a sham. And, unlike conspiracy theories, climate change science has a reliable—if frightening—habit of being confirmed by reality. In early December, the World Meteorological Organization reported that the last decade has in fact been warmer than either the 1980s or the 1990s, and that 2009 will likely be the fifth warmest year since the instrumental record began in 1850.
This graph shows increases and decreases in average global temperature compared to the mean temperature from 1961-1990. Notice that individual years might be warmer or colder than the preceding year, but despite this variability, the most recent five-year trend is upward. Skeptics have claimed that recent fluctuations represent a cooling trend, but 2009 was one of the warmest years since record keeping began. (Source: Global Warming Art)
Still, if you thought the United States seemed particularly cold this fall, you're right. A surface temperature analysis from NASA shows that in October, most of the world experienced warmer than normal temperatures. But North America and Northern Europe were actually cooler. This is completely consistent with climate science, which predicts that the world's mean temperature will increase over time due to increasing greenhouse gases in the atmosphere, and allows for all sorts of anomalies in space and time.
Global temperature anomalies in October 2009. Severe warming (dark red) was most dramatic in the arctic region, while parts of North America, Europe and Antarctica were somewhat cooler than long-term averages. Pockets of cooling in an otherwise warming world are consistent with climate change predictions. (Source: Goddard Institute for Space Studies Surface Temperature Analysis, NASA)
As for your concern about lower crop yields, first I checked the latest world crop forecasts published by the USDA, and couldn't find mention of a projected 10 percent drop in crop yields. They don't provide data on combined crop yields, but rather they break it down by individual crops. For example, the latest report says wheat yields are up and rice yields are down. Next I spoke with David Lobell, a Stanford professor and a fellow at Stanford's Center on Food, Security and the Environment, and he also hadn't heard of a projected 10 percent drop in crop yields due to global cooling. He did have this to say though: "Colder temperatures generally lead to increased crop yields." So, I'm sorry to break it to you, but the world is not cooling, and if it were, crop yields would likely increase anyway.
I'm glad you brought up the fact that the world's atmospheric carbon dioxide is not entirely manmade, though. CO2 is a normal part of our atmosphere, and prior to industrialization in the 1800s, CO2 levels hovered around 280 parts per million. Now the atmosphere has 384 parts per million CO2 due to human influences such as the burning of fossil fuels and land-use changes. Sure, the animals and volcanoes and all the other non-human sources have kept pumping out their share of greenhouse gasses. But we've increased our share on top of that baseline, and that's what's tipping the balance. The negative impacts include more high intensity storms, loss of biodiversity, water shortages and heat waves.
But your real question is, how can we justify the cost of minimizing CO2 emissions. Getting into the details of the technology and expenditure needed for that task is probably best left for another column or three, but a lot of what we need is already available and more is being developed every day, including right here at Stanford. Green technology development will almost certainly be the next big engine of economic growth, and the Chinese, Germans and others will be glad to take the lead if we don't.
So how can we justify the effort and cost? Take the reality of climate change, add a dash of caring for your fellow humans and the future the Earth, and mix in a nice splash of economic opportunity—can we justify not taking action now? That should give us all plenty to think about the next time we're walking home in the cold.
Nicholas Jachowski plans to receive his bachelor's and master's in earth systems in 2010.
