Image by Paul Hammond

97 percent of scientists said that humans evolved over time, but 28 percent of the American public believes that scientists have not come to a consensus on evolution.

The statistics on climate change are similar. 84 percent of scientists agree that the earth is getting warmer due to human activity, but 35 percent of the American public think that scientists have not reached a consensus on the influence of human activity on global warming.

In both cases scientists have reached an overwhelming consensus, yet one third of the general public thinks that scientists are debating these issues!

This suggests that scientists need to do a better job educating the public - and by educating I don’t mean a discourse on how atmospheric carbon dioxide levels contribute to increases in average global temperatures and ocean acidification. I mean that scientists need to do a better job discussing scientific consensus with the public (though the former is also important).

For example, I have a colleague who doesn’t think that human activity contributes significantly to global warming. He also thinks that there is no scientific consensus on the issue. Perhaps my time would be better spent convincing him that there is, in fact, scientific agreement on the human causes of global warming, instead of delving into the science of climate change.

On the other hand, what is scientific consensus? 2533 scientists-representing the fields of biology and medicine, chemistry, geosciences, and physics and astronomy-were surveyed by the Pew Research Center for the People & the Press and the American Association for the Advancement of Science. About half of the scientists were in biological and medical sciences, which some might argue are as related to geosciences as art is to astronomy. (As a biologist, I knew nothing about climate change before coming to the State Department.)

Pew surveyed scientists and non-scientists in the United States. Although the survey was conducted in English and Spanish, no doubt the results represent a U.S. view. How would scientists and the public react outside the U.S.?

Image by TWW

TWW's house in Brazil, with a white roof, stands out among the neighbor's darker roofs.

Last week I discussed the science behind Secretary of Energy Steven Chu’s comment that making roofs white will conserve energy and reduce global warming.

This photo depicts this scientific principle in action: TWW in Brazil painted her roof white. It looks great, even among a sea of dark colored roofs.

Many thanks to TWW and other readers for submitting their comments. I’m working on a series of features explaining the science behind climate change, so stay tuned!

Image by trillbilly

A house in Bermuda with a white roof.

In an interview with the British newspaper The Independent, Chu said:

“If you look at all the buildings and make all the roofs white, and if you make the pavement a more concrete-type of color than a black-type of color, and you do this uniformly … It’s the equivalent of reducing the carbon emissions due to all the cars in the world by 11 years.”

Let’s tackle energy conservation first. On a hot day, you’ll be much cooler wearing a white shirt than a dark shirt. This is because light colored objects reflect more sunlight. Dark objects absorb more sunlight than light colored objects; the absorbed light then radiates away from the object (or is emitted from the object) as heat. Your dark shirt is absorbing sunlight, and then releasing it as heat, which makes you feel hotter.

Image by Cool Roof Rating Council

A white roof reflects more light and radiates less heat than a dark roof.

A dark roof on a building is like a dark shirt. The roof absorbs sunlight, and then radiates heat into the building. The temperature inside the building increases, and we use energy - in the form of air conditioning - to cool the building. Paint the roof white (or use a reflective material, like white tiles), the roof absorbs less sunlight, less heat is radiated into the building, the temperature inside the building doesn’t increase as much and we don’t need to use as much energy to cool the building. That’s how painting a roof white conserves energy. In the United States, the California state government has become a leader in encouraging the use of white roofs or cool roofs.

White roofs may also reduce global warming.

When sunlight is absorbed by a roof, the roof heats up and radiates heat in the form of  infrared light, which is invisible to humans (it has a longer wavelength than red light). Infrared light is emitted from the roof and reaches the atmosphere, where it is absorbed by gases and re-emitted as infrared light - a continuous cycle of absorption and emission that traps heat in the atmosphere and increases the temperature of the Earth. Gases that absorb and radiate infrared light are called greenhouse gases - these include water vapor, carbon dioxide and ozone.

Atmospheric gases don’t absorb much visible light, which is why sunlight reflected from a white roof - visible light - can travel through the atmosphere and escape into outer space.

Image by redskunk

These principles also apply to car roofs.

Incidentally, light is also absorbed by the Earth - the ground, the soil - and returned to the atmosphere as infrared light, where it is trapped as heat. This is the greenhouse effect. We can’t paint the Earth white to reduce global temperatures, but nature has helped us out a bit, in the form of ice. Polar ice caps and glaciers are like big, white roofs - they reflect much of the incoming sunlight back into the atmosphere and out into space. Scientists and policymakers are concerned that melting ice will expose land, decreasing the amount of sunlight reflected back into space and increasing the amount absorbed by the Earth and trapped in the atmosphere as heat.

Researching this post I have found no reason why we should not be painting our roofs white (or using reflective tiles). Can you think of a reason not to do this? People might complain about having to look at a white roof, but does an aesthetic concern outweigh conserving energy and reducing global warming?

From May 26 - 29, Nobel Laureates from across scientific disciplines were joined by world experts in climate change to discuss “the connections between global warming and other urgent environmental, economic and development challenges facing our world.” The symposium was hosted at The Royal Society and St. James’s Palace in London, under the patronage of the Prince of Wales. 

Steven Chu, the Nobel laureate who now leads the U.S. Department of Energy, attended the symposium and held interviews with the British media.

One of my favorite interviews is with Channel 4, where Chu discusses the cultural shift that must occur to spur Americans to use more renewable energy.  Chu said “the young people get it” and added that just as the young generation helped convinced their parents to quit smoking, so too the current young generation will urge their parents to change their behavior to better protect the environment. Chu advocates rapidly deploying existing energy efficient technologies.

I think it’s safe to say that the United States is now fully engaged in climate change.

Then again, I’m a biased source.