The 2007 report by the Intergovernmental Panel on Climate Change estimated a 95% chance that global warming is real and not a passing anomaly, and a 90% chance that human activity is a significant contributing factor. Does that mean they don't know?
The truth is ... cloudy.
More below the fold....
Governing Science, Part II - Climate Mysteries and Myths
This week Morning Feature considers Richard Muller's Physics for Future Presidents: The Science Behind the Headlines, a primer on the science underlying political issues. Yesterday we looked at terrorism and safety. Today we consider what we know, and what we don't, about global climate change. Tomorrow we conclude with climate and energy solutions based in physics rather than fear or fantasy.
Disclaimer: I am not a physicist. Dr. Muller is a professor of physics at Berkeley, and teaches a course on this topic. This is a shorter version of his textbook, written for a general audience. Even so, there is far more material than I can cover in three essays, and any errors are my own.
The Case of the "Charismatic Fauna"
Most of us have heard about polar bears drowning because the polar ice is melting. A new ad for the Nissan Leaf, an all-electric car, plays on that with the image of a polar bear traveling from the arctic to embrace a Leaf owner:
It's a charming ad. But Dr. Muller, a peer reviewer for the IPCC study, argues this is one of many myths surrounding climate change. In fact, the ad incorporates three myths:
Myth: Many polar bears have drowned due to melting polar ice, because they cannot swim from one ice floe to the next.
Fact: A lawsuit was filed in Britain regarding this claim. The judge found evidence for only four drowned polar bears, all of whom were caught in a flash flood.
Myth: Decreasing polar ice caps are irrefutable proof of global warming models.
Fact: The models predict exactly the opposite, that warmer ocean temperatures will yield more seawater evaporation, thus more precipitation. Because the 1°F of warming measured so far leaves the polar regions well below freezing most of the year, the extra precipitation should come as snow and result in more ice, not less. Polar ice is melting at a faster-than-expected rate, but the climate change models don't yet explain why.
Myth: Electric cars have no carbon emissions.
Fact: It depends on how the electricity was generated. If the car batteries were charged with electricity from a coal or oil fired plant, the emissions moved from the car's tail pipe to the plant's smoke stack. Worse, because energy is lost in transmission from plant to plug and even the best batteries are inefficient, an electric car charged from a coal or oil fired plant may have more emissions than a gasoline car.
The Case of the Inconvenient Graphs
Dr. Muller applauds Vice President Al Gore for An Inconvenient Truth, which brought climate change science into the mainstream public debate. However, Dr. Muller notes that some of the graphs in the book are misleading, or are based on findings that have been challenged and changed since the book's publication. For example:
Myth: Ice core samples show that throughout earth's history, rising temperatures have followed rising atmospheric CO2 levels.
Fact: Until the modern era, the relationship of CO2 and temperature is exactly the reverse: rising CO2 levels followed rising temperatures. Ice core samples show an 800-year lag of rising CO2 behind rising temperatures, because cold water can hold more CO2 than warm water. Warming oceans released dissolved CO2 into the air, a process that took about 800 years. Rising CO2 levels from human activity are very likely contributing to rising temperatures now, but that wasn't the relationship before humans began burning fossil fuels.
Myth: Hurricanes are causing more damage due to global warming.
Fact: The insurance industry graph that Vice President Gore uses (page 102) is not adjusted for inflation, coastal population, or the increasing cost of coastal buildings. When those are factored in, the damage due to hurricanes shows spikes for very severe storms (the 1928 Okeechobee hurricane is the highest), but no clear upward trend. The apparent increase in named hurricanes and severe (Category 4 or 5) hurricanes may be due to our ability to detect and measure (with satellites) storms at sea that would not have been counted in past decades.
Myth: The "hockey stick" graph shows flat temperatures over the past 1000 years, and sharply rising temperatures today, proving global warming.
Fact: There was a mathematical flaw in the program that generated the "hockey stick" graph. Dr. Muller explains the analytical method used in the program (page 204), but the the program minimized variations in historical climate data. When the graph is redrawn with the correct variations, the temperatures over the past 1000 years were not as flat as shown, so today's temperature increases - the "blade" of the "hockey stick" - are not quite as unprecedented or dramatic.
The Case of the Cloudy Conclusions
Climate change deniers have jumped on such inconsistencies, along with the IPCC's not-quite-100% certain conclusions, as proof that climate change is a hoax. It's worth noting that many of the same people applauded the "One Percent Doctrine" - if there is even a 1% chance of a terrorist threat, we must treat it as a certainty - yet ignore the IPCC's 95% chance that climate change is real, and the 90% chance that human activity is a major contributing cause. The deniers simply use statistics as excuses to justify their preexisting beliefs.
But why are the IPCC only 95% confident that climate change is real, and only 90% confident that human activity is a contributing cause? The answer, in a word, is clouds.
Climate scientists don't yet fully understand why and how clouds form and move, or the exact relationship between cloud density and earth temperature. Clouds both reflect some sunlight back into space and trap some heat in the atmosphere; that's why it's cooler on a cloudy day, but warmer on a cloudy night. The historical data for clouds is spotty, and scientists are still working to develop models that reliably predict cloud formation and temperature effects.
Despite some media myths and mistaken graphs, and the uncertain effects of clouds, climate scientists are extremely confident (95% chance) that climate change is not a passing anomaly but a real event, and very confident (90% chance) that human activity is a major contributing cause.
The real question is what we can do about it, and we'll discuss that tomorrow.
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