Baking in the heat this summer? Population growth in urban areas promises to cause substantial warming in those "megapolitan" urban areas due to changes caused by replacing nature with buildings and roads.
TEMPE, Ariz. – According to the United Nations' 2011 Revision of World Urbanization Prospects, global urban population is expected to gain more than 2.5 billion new inhabitants through 2050. Such sharp increases in the number of urban dwellers will require considerable conversion of natural to urban landscapes, resulting in newly developing and expanding megapolitan areas. Could climate impacts arising from built environment growth pose additional concerns for urban residents also expected to deal with impacts resulting from global climate change?
In the first study to attempt to quantify the impact of rapidly expanding megapolitan areas on regional climate, a team of researchers from Arizona State University (ASU) and the National Center for Atmospheric Research has established that local maximum summertime warming resulting from projected expansion of the urban Sun Corridor could approach 4 degrees Celsius. This finding establishes that this factor can be as important as warming due to increased levels of greenhouse gases. Their results are reported in the early online edition (Aug. 12) of the journal Nature Climate Change.
I think population growth is a net negative given the number of people already here. The external costs outweigh any benefits as natural resources deplete and more land gets shifted to human uses.
White roofs would cut the warming in half. But the warming would still be large.
"The worst case expansion scenario we utilized led to local maximum summer warming of nearly 4 degrees Celsius. In the best case scenario, where Sun Corridor expansion is both more constrained and urban land use density is lower, our results still indicate considerable local warming, up to about 2 degrees Celsius," Georgescu said.
An additional experiment was conducted to examine an adaptation where all of the buildings were topped by highly reflective white or "cool" roofs.
"Incorporating cool roofs alleviated summertime warming substantially, reducing the maximum local warming by about half," Georgescu said. "But, another consequence of such large-scale urbanization and this adaptation approach include effects on the region's hydroclimate."
The cool roofs, like the maximum-growth scenario without this adaptation approach, further reduce evapotranspiration – water that evaporates from the soil and transpires from plants. Ultimately, comparison of summertime warming resulting from Sun Corridor expansion to greenhouse-gas-induced summertime climate change shows that through mid-century the maximum urbanization scenario leads to greater warming than climate change.
At least in terms of deltas from the pre-industrial era soot pollution is now seen as having a bigger warming effect than methane.
DENVER, Aug. 31, 2011 — A new study of dust-like particles of soot in the air — now emerging as the second most important — but previously overlooked — factor in global warming provides fresh evidence that reducing soot emissions from diesel engines and other sources could slow melting of sea ice in the Arctic faster and more economically than any other quick fix, a scientist reported here today.
In a presentation at the 242nd National Meeting & Exposition of the American Chemical Society (ACS), Mark Z. Jacobson, Ph.D., cited concerns that continued melting of sea ice above the Arctic Circle will be a tipping point for the Earth's climate, a point of no return. That's because the ice, which reflects sunlight and heat back into space, would give way to darker water that absorbs heat and exacerbates warming. And there is no known way to make the sea refreeze in the short term.
Soot landing on ice lowers its albedo. In other words, soot, being dark, absorbs light that ice would otherwise reflect. Making ice darker causes more sunlight to be absorbed, heating and melting the ice.
What is good about this result: Soot is bad for our health. We should want to cut its emissions anyway. The global warming debate isn't even something you need to care about to want to cut soot pollution from diesel trucks, coal-burning electric generator plants, and other sources.
Jacobson's calculations indicate that controlling soot could reduce warming above parts of the Arctic Circle by almost 3 degrees Fahrenheit within 15 years. That would virtually erase all of the warming that has occurred in the Arctic during the last 100 years.
"No other measure could have such an immediate effect," said Jacobson, who is with Stanford University. "Soot emissions are second only to carbon dioxide (CO2) in promoting global warming, but its effects have been underestimated in previous climate models. Consequently, soot's effect on climate change has not been adequately addressed in national and international global warming legislation. Soot emissions account for about 17 percent of global warming, more than greenhouse gases like methane. Soot's contribution, however, could be reduced by 90 percent in 5-10 years with aggressive national and international policies."
Keeping the Arctic (and Antarctic) cold is more important than keeping temperatures down in lower latitudes. Keep the ice as ice and we can keep our coastlines from submerging.
The quickest, best way to slow the rapid melting of Arctic sea ice is to reduce soot emissions from the burning of fossil fuel, wood and dung, according to a new study by Stanford researcher Mark Z. Jacobson.
Since soot is bad for human health soot emissions reduction ought to go the head of the line of methods for cutting global warming. Even people who question the anthropogenic global warming theory should be able to see soot reduction as good public policy.
Only carbon dioxide causes a bigger warming effect.
His analysis shows that soot is second only to carbon dioxide in contributing to global warming. But, he said, climate models to date have mischaracterized the effects of soot in the atmosphere.
Because of that, soot’s contribution to global warming has been ignored in national and international global warming policy legislation, he said.
"Controlling soot may be the only method of significantly slowing Arctic warming within the next two decades," said Jacobson, director of Stanford’s Atmosphere/Energy Program. "We have to start taking its effects into account in planning our mitigation efforts and the sooner we start making changes, the better."
One estimate puts the number who die in the US each year from diesel soot at 21,000 people. Soot boosts the risk of lung cancer, heart disease, and other diseases. Soot elevates blood pressure. So I'm very keen to cut soot emissions.
A reduction in soot emissions would cool the Arctic.
Jacobson found that eliminating soot produced by the burning of fossil fuel and solid biofuel could reduce warming above parts of the Arctic Circle in the next 15 years by up to 1.7 degrees Celsius. For perspective, net warming in the Arctic has been at least 2.5 degrees Celsius during the last century and is expected to warm significantly more in the future if nothing is done.
The most immediate, effective and low-cost way to reduce soot emissions is to put particle traps on vehicles, diesel trucks, buses, and construction equipment. Particle traps filter out soot particles from exhaust fumes.
Soot could be further reduced by converting vehicles to run on clean, renewable electric power.
Biofuels burned by poor people in villages of undeveloped countries kills many more people than fossil fuel soot.
Jacobson found that although fossil fuel soot contributed more to global warming, biofuel-derived soot caused about eight times the number of deaths as fossil fuel soot. Providing electricity to rural developing areas, thereby reducing usage of solid biofuels for home heating and cooking, would have major health benefits, he said.
Short of electrification distribution of inexpensive but highly efficient wood-burning stoves could make a big difference.