Scientists studying urban heat islands in 42 cities in the Northeastern U.S. have found that the greatest temperature differences between urban areas and the surrounding environment are in places you might not expect.

Cities located in forest environments have higher heat island effects than those in grasslands or deserts. The bigger the city, the greater the heat island effect. And the more densely-populated cities are worse off than the sprawling ones in this respect.

The results may seem counterintuitive. Isn’t sprawl supposed to be bad? And in one city – Las Vegas – the heat island effect was actually negative in one study, meaning its temperature was lower than the surrounding desert environment. That’s not because of all the water fountains at the Venetian or the Mirage casinos.

“People tend to have some trees, or parks, or lawns around the house or in the street and that’s why the temperature in Las Vegas is sometimes cooler than in deserts because there’s not much vegetation in the deserts,” said Ping Zhang, a research scientist at NASA’s Goddard Space Flight Center.

Zhang says the differences in heat effects come down to the amount of vegetation a city has. Densely populated areas tend to have less vegetation than cities that sprawl. That makes the more compact Providence, Rhode Island, have almost double the heat island effect of the more sprawing Buffalo, New York, despite their similarly-sized populations.

These differences have a big impact on urbanites. About half the world’s population lives in cities, an amount expected to increase to 80 percent by 2030. Hotter cities can exacerbate the effects of heat waves, which are increasing in frequency and intensity because of climate change.

Air conditioning is unlikely to make the circumstances better, said Cecíl de Munck of the National Center of Meteorological Research in France. Parisians still sweating over the 2003 heat wave, which killed more than 5,000 people, may turn to air conditioning as heat waves hit more frequently. But doing so would increase the city’s outside temperature by as much as 3.6 degrees Fahrenheit because of all the hot hair venting from AC units.

“We are faced with a vicious cycle since an increase in air temperature leads to an increase in demand,” de Munck said.

Best thing to do? The scientists agree that the answer is planting more vegetation.

Alison Hawkes is a freelance journalist in San Francisco and co-founder of Way Out West News.

Some say storing carbon underground as a way to curb greenhouse gas emissions is risky. The container has to last essentially forever, and what if an earthquake rips through the seal? But new research is showing that pumping CO2 underground could itself trigger earthquakes.

Stanford University geophysicist Mark Zoback looked at saline aquifers, one of the main types of geologic formations under assessment for carbon sequestration. He found that adding CO2 gas could increase the geologic pressure underground and set off a quake. Not a big one, mind you. Most likely you’d feel some shaking on the surface at a magnitude three or four. But underground the scenario would be a different story.

“At depth those earthquakes represent slip-on faults and if those earthquakes threaten the integrity of the geologic seal that’s keeping the CO2 in place, then they pose the hazard of inducing long-term leakage of the CO2 out of the repository,” said Zoback. “And of course that’s why it’s being injected in the first place, to keep it out of the atmosphere.”

The Earth’s crust is brittle because of shifting continental plates and just a bit more pressure can set off a quake in otherwise seismically safe areas. Never mind quake-prone California,” he said. “Even quiet places that have been eyeballed for carbon storage like the Midwest still have fault lines.”

To make a dent in global warming using carbon sequestration, about a billion tons of CO2 per year needs to be pumped underground by mid century – equivalent to the volume produced by burning oil and gas. Zoback figures that represents about 3,500 storage sites, or 75 new projects per year by 2050. He’s skeptical that all those sites can be found: “Are we going to invest the huge sums, we’re talking about many tens of billions of dollars only to find that when the earthquakes start occurring we’re going to have to stop the injection and find alternative strategies?”

Zoback presented his findings at the American Geophysical Union’s Fall Meeting in San Francisco.

Alison Hawkes is a freelance journalist in San Francisco and co-founder of Way Out West News.

Carbon capture demo at the annual American Geophysical Union meeting. Photo: Molly Samuel

Almost lost amid the Copenhagen media clutter was last week’s meeting of the American Geophysical Union in San Francisco. So this week we’re playing a little catch-up. Lauren Sommer has the second of three posts on things that caught our attention at AGU.

Carbon capture technology has largely focused on the most convenient emissions sources–namely the stacks at large power plants. But as Columbia University’s Allen Wright showed at the American Geophysical Union conference in San Francisco last week, there are other ways to do it.

Wright and colleagues demonstrated their “air capture” technology, where carbon dioxide is absorbed straight from the air by something that looks a lot like a gadget for cleaning Venetian blinds. It’s a special plastic material with a sponge-like consistency. Once the carbon is absorbed, the material is exposed to water or water vapor which causes the carbon to be released. It can then be captured. Wright says it captures CO2 three to five times better than a leaf in full sunlight.

On a large scale, this technology might be built into “artificial trees” that could be stationed anywhere around the globe. The prototype, designed by Wright’s Global Research Technologies, doesn’t look much like a tree. It’s a shipping container with a circular, rotating basket on top where the air capture units are exposed to the air. After one rotation, the baskets would be brought “downstairs” where the carbon is captured. From there, the carbon could be geologically sequestered or even used to make beverages bubbly.

Of course, the main criticism of this approach is efficiency. Carbon dioxide is only about 0.04% of the atmosphere, which is why more concentrated sources like power plant stacks get more attention. Wright says capturing carbon from power generation will be important, “but capture at the stack isn’t enough. It won’t do what has to be done. Air capture has the advantage of being able to deal with emissions from anywhere on the planet from any source.”

Cars are one of the sources he’s talking about. Their prototype unit is designed to capture a ton of carbon a day, which would neutralize the emissions from about 20 cars. They hope to get the cost of each carbon-capturing unit down to the price of car, so the cost of reducing a ton of carbon could one day be similar to other technologies.

Still, to make an impact on global emissions, millions of these units would need to dot the landscape. And just as with renewable energy, NIMBY issues are a potential roadblock. But as is a common refrain these days, Wright says if we’re serious about cutting emissions, we’ll need every technology that shows promise.

Climate researcher Dan Cayan, from the Scripps Institution of Oceanography, described California as “extra vulnerable” to climate change and gave a broad (and somewhat scary) overview of the reasons why. The state’s temperature increases are expected to be similar to the global average temperature rise in the coming decades, making for hotter summers with longer heat waves. Given the expected increase in population in California’s interior, longer and harsher heat waves could have significant public health implications.

On top of the more intense summers and milder winters, precipitation across the state may well decrease, especially in Southern California. These drier conditions will be compounded by a significant withering of the Sierra snowpack. Even with a moderate increase in temperature (2 degrees C), Cayan says more than half of the historic California snowpack will disappear by 2100, as the mountains get more rain than snow at higher elevations. That can increase flooding and coupled with expected sea rise over the next century, the San Francisco Bay and the Sacramento/San Joaquin Delta may be in for some extreme events.

Fortunately, others are looking into sea level rise and what it’s going to mean for the San Francisco Bay Area and the coast of California. Peter Gleick, president and founder of the Pacific Institute, spoke about a new study currently under review focused on the projected impacts of sea level rise, including flooding and erosion, and the potential responses. The study will evaluate flood and erosion potential, create detailed maps of California’s vulnerable areas, estimate risks to populations and structures, anticipate costs of various adaptation strategies, and make policy recommendations. Gleick cited one immediate need as a catalog of the state’s existing levees and their conditions.

The report’s results should be out in February, which is also when we should see the draft version of the first California Adaptation Strategy, which aims to compile information on expected climate change impacts for the state and provide policymakers and resource managers with strategies for addressing them.