Summer 2012, like most summers in recent memory, has brought an assortment of extreme weather that is becoming familiar – record-breaking fires (this time in Colorado), an iceberg twice the size of Manhattan breaking off of Greenland’s Petermann Glacier, and June was the 328th consecutive month with a global temperature higher than the 20th century average. Events like these raise the question of whether the humans who live in industrialized societies like the United States understand that the planet we live on is warming. Two recent articles explore this topic in a really helpful way.


NASA scientist James HansenNASA’s James Hansen, who has long been at the forefront of global warming science, tackles the slippery question of human perception of global warming as an important practical matter. In the draft of a new paper Hansen and two co-authors discuss the “practical implications of this substantial, growing climate change,” specifically when and how the “informed public” will recognize a warming pattern. It is as though Hansen, whose work in the 1960’s and 70’s focused on the atmosphere of Venus, is observing another planet and its inhabitants — when will the human inhabitants of Earth, with their advanced language and tools, understand what is going on around them? The practicality of this question is clear: action follows from perception.

In 1988 Hansen himself speculated that unusually warm summers and mild winters would have occurred frequently enough by the early 21st century for the public to perceive a change, even understand that we are moving to a new normal. With striking images,Surface temperature anomalies Hansen and his co-authors show that extremely high temperature abnormalities, which should occur on only 0.1 – 0.2% of the planet’s surface, are consistently occurring on 4 – 13% of the Earth’s surface every summer (click to enlarge the image on the right, brown areas represent temperatures greater than 3 standard deviations from the average).

Hansen and his co-authors also consider the possibility that, in addition to the temperature outside, changing patterns of precipitation might influence human perceptions. Climate models predicted what we’re experiencing — as Global Climate Change Impacts 2009 Reportthe planet warms extreme precipitation events intensify — droughts become more extreme as heat increases pressure in areas already prone to drought, and hard rains become floods more frequently because a warmer atmosphere also holds more moisture. In the paper’s conclusion, Hansen even wonders if individuals in other regions of the country are seeing changes specific to their surroundings that might correspond to what he sees at his home in Pennsylvania: distressed birch, oak, ash, and maple trees that once grew wild but now require watering to survive longer, hotter summers.


Bill McKibben, as usual, guides the conversation to the crucial question: “Now what?” His feature in the August 2 Rolling Stone is the sort of thing that ought to be read and discussed widely. After a sobering review of three numbers everyone should understand, McKibben makes a case for naming the planet’s enemies. First a quick summary of McKibben’s numbers: 2 degrees Celsius is the rise in average surface temperature (about 3.6 degrees Fahrenheit) that was considered the outer limit of what the planet could endure and still maintain ecosystems similar to those that have existed in the Holocene era (the last 12,000 years). We’ve already seen an increase of 0.8 degrees Celsius and based on changes thus far many scientists now think that 2 degrees is more than we can handle (James Hansen says it is “long term disaster”). But the goal of 2 degrees Celsius is what 167 countries signed off on at the 2009 Copenhagen summit, and it’s a good starting point for a conversation.

McKibben’s next two numbers answer the “Now what?” question. 565 gigatons is an estimate of how much carbon dioxide we could put in the atmosphere and stay within the 2 degrees Celsius goal. 2,795 gigatons is how much carbon dioxide the world’s oil, coal, and gas reserves contain. So, while scientists debate whether the planet can stand another 565 gigatons, we are on track to put five times as much into the atmosphere. The solution is actually simple. We need to leave most of that oil, coal, and gas in the ground. The enemies of the planet, McKibben argues, are the oil companies (Exxon-Mobil, BP, Chevron, etc.) and coal companies (Severstal, BHP Billiton, etc.) that are ready to bring these fossil fuels above ground, even as they understand that the Earth will be Severstal coal plant (Russia)transformed into something out of science fiction as a result. The momentum to move these fossil fuels above ground is strong. McKibben points out that while the oil, coal and gas are physically underground they are economically already with us, reflected in the balance sheets, future profits, and stock values of the companies that have made claim to them.

Put it all together and the message is clear — when we notice the natural world we’ll notice a warming planet; when we understand the science we will not only begin to understand the scope of the danger, but also see where that danger is coming from. Again, to appreciate the clarity of McKibben’s argument it is well worth reading his Rolling Stone piece in full.


Global warming will define the industrial age, and may ultimately come to define humans as a species. It really is necessary that we understand the basics of the science. We owe it to each other and to future generations. I used to teach 9th grade World Geography, including a long unit on the causes and effects of climate change. I always told the students that by the end of the unit they were going to be able to explain something that most adults in their lives only pretended to understand. Of course it is absurd that there is still a debate in the United States about whether humans are causing the planet to warm, but it’s also true that many who accept the scientific consensus aren’t actually able to explain the basics of that consensus. Maybe that’s part of the problem.

It’s debilitating to political culture in the U.S. that we’re loathe to admit uncertainty or deficits in our knowledge — as though it’s embarrassing to be a lifelong learner. In the spirit of lifelong learning, I’d recommend a website that I found extremely helpful for teaching the science of climate change — NASA’s Eyes on the Earth. The presentation is sophisticated but easily understandable — perfect for clarifying the science and starting conversations.