Buying Time on Climate Change

While much of the discussion of climate change revolves around carbon dioxide because of its primary role in increasing average global temperatures, many other chemicals other than CO₂ can have an effect on the climate. Two such important contributors to global climate are the greenhouse gas methane (i.e. the primary component of natural gas) and black carbon (soot from incomplete burning). Methane is emitted by a variety of sources both natural and human such as wetlands and rice paddies, as I had discussed in a previous article about the methane cycle. Black Carbon is nothing more than the smoke common in wood fires or any kind of incomplete burning from diesel or coal burning. It also can absorb heat in the atmosphere and cause warming, and when deposited on snow or ice, can decrease its cooling ability by reducing its albedo or how much light it reflects. Both methane and soot have much shorter lifetimes than carbon dioxide in the atmosphere, at 11 years and weeks to months respectively compared to 170 years for carbon dioxide, making them attractive targets for short to medium term reductions in emissions related to climate change.

In addition to their effects on climate, methane and black carbon are also problematic emissions because they both act as precursors to photochemical smog and because black carbon is a big component of particulate emissions that are really bad for your lungs. Because reducing both these emissions would have a public health benefit beyond any changes to the climate, emission reductions of methane and black carbon could potentially be an important first stem to slowing climate change. In a recent Science article (gated), Drew Shindell, a NASA scientist, and a team of scientists and economists from around the world identified various technologies available now and possible regulations that could reduce methane and black carbon emissions immediately. They then calculating the costs of of implementing these new technologies and compared them to the potential benefits on public health, crop yields, and climate. The benefits of reducing both far outweighed the costs, in reduced impacts from changes in climate from differences in precipitation patterns, crop yields, and premature deaths. In particular, the reductions in black carbon resulted in an enormous benefit in terms of reduced premature deaths since particulate emissions such as black carbon are pretty bad for human health. Most of the benefits were realized in India and China (where black carbon emissions are much, much worse than in the United Stats or Europe) in the form of avoided changes in the precipitation patterns crucial for agriculture. However, the United States also benefited from potential increases in crop yields due to less photochemical smog from methane emissions. The ozone formed in photochemical smog, in addition to being a lung irritant, also reduces crop yields. Plants reduce atmospheric uptake in high concentrations of ozone because of its highly reactive nature, which can damage the inside of the plant as easily as it can damage your lung tissue.

For climate change, the full implementation of their recommended technologies and regulations would actually in the short to medium term help slow the pace of climate change relative to a "business as usual" scenario. This interactive graphic from NASA that accompanied this publication shows how under different "climate sensitivity" (how much the temperature changes in response to increased CO₂) scenarios the implementation of CH₄ (methane) and BC (black carbon) measures can reduce the expected warming. Depending on how sensitive the climate is to changes in CO₂ these measures delay the time it takes to reach 2^oC degree warming threshold that many scientists consider to be a dangerous threshold for the climate. This gives all of us some "breathing room" (so to speak) to develop alternatives to fossil fuel burning as a source of energy because even with these measures CO₂ is still the primary mover of climate change. Many times it's extremely under-appreciated just how challenging it is to develop alternatives to fossil fuels as it may be decades before a true alternative can be developed. This study gives us hope that we can eventually tackle climate change without dramatic changes to living standards or a halt to the increasing prosperity that free trade and liberalizing reforms are bringing to the developing world.

Related Links:
An interview with Drew Shindell, the primary author of this study

Climate Change, Photosynthesis, and El Niño

The way carbon is moved between the atmosphere, the biosphere, oceans, and other parts of the Earth system plays an important role in the current scientific consensus on climate change. While the various processes involved are known well enough to predict that the planet will continue warming if CO₂ concentrations keep increasing from fossil fuel emissions, better understanding of any part of the so-called carbon cycle can improve predictions of how exactly how much warming will occur. The image below shows a model of the carbon cycle.

In particular, the approximation of the conversion of CO₂ to sugars by plants during photosynthesis (called primary production) could have its range of possible quantities narrowed. In a recent study in the journal Nature, the authors use measurements the rare, stable oxygen isotope, oxygen-18, in CO₂ to estimate the value of primary production. Since CO₂ can exchange oxygen atoms with water in leaves without undergoing photosynthesis, the ratio of oxygen-18 to oxygen-16 in CO₂ is related to how much CO₂ is converted to sugars in plants. Using these measurements, they actually found that primary production might be greater than previously thought! Their estimate has the advantage of not relying on assumptions about biology and provides further constraints on primary production. This increase in the estimate of primary production certainly may turn out to be good news because it could mean that CO₂ concentrations will rise (slightly) more slowly. However, especially because primary production does not count how much of the sugars produced are consumed by the plant itself (and thus changed back into CO₂), it does unfortunately not mean that the biosphere can completely offset all changes in CO₂ from fossil fuel emissions.

By observing the oxygen-18 to oxygen-16 ratio over 30 years at various locations around the world, the scientists found occasional small increases in the ratio from year to year. Oddly enough, these increases occurred at the same time as El Niño! They explained this increase in the oxygen-18 to oxygen-16 ratio by decreases in rainfall over rain forests (where lots of photosynthesis occurs) in Southeast Asia and northern South America during El Niño. Because the water with oxygen-18 is "heavier" than water with oxygen-16, the water in clouds tends to have more oxygen-16 since "lighter" oxygen-16 containing water evaporates first. During periods with less rainfall, the water still evaporates over rainforests, reducing the amount of oxygen-16 in water in the soil. Without enough rainfall to return oxygen-16 back to the ground, the relative amount of oxygen-18 increases, thus the water in plant leaves also has more oxygen-18. Although this effect is very small (a 0.05% change), it can be measured in CO₂. As the southern ocean returns to a La Niña pattern and rainfall in these regions increases, the oxygen-18 to oxygen-16 ratio in CO₂ eventually returns to its "normal" level. The scientists used the rate of change in oxygen-18 to calculate an estimate of primary productivity. Additional measurements of oxygen-17 to oxygen-16 ratios may provide additional constraints to help improve this estimate further. (For a more detailed explanation of isotopes in geology and chemistry, see this previous post)

(h/t Jeremiah J.)

Extreme cold and global warming

"Hey! There was some crazy blizzards in the US this year and the last. How can you scientists still say that the Earth is warming when it was unusually cold in the winter of 2010 and 2011?" This is a common kind of question from laymen in regards to the feasibility of climate change. Luckily, some scientists actually looked at this in a recent article in Geophysical Research Letters. (gated beyond the abstract, unfortunately)

These scientists divided the Northern hemisphere into eight regions: USA, Canada, Alaska/Yukon, Siberia, Far East, Central Asia, Nothern Europe/Russia, and Mediterranean/Middle East. Then, using statistical techniques, they examined the temperature record for extreme cold and warm events for the winters of 2010 and 2011 and compared it to the historical record for 1950-2009. Indeed, the USA, Northern Europe, and Siberia did experience winters that were unusually cold in 2010 and 2011. However, the number and extent of unusually cold days in these two regions was offset by an even greater number of unusually hot days in every other region of the Northern Hemisphere! Not only were there are larger number of extremely hot days, but these hot spells also lasted much longer and were more extreme compared to any of the extremely cold days in the United States, Europe, or Siberia.

What accounted for the cold extremes experienced in parts of the Northern Hemisphere then? Similar to the natural El Niño/El Niña phenomenon in the Southern Pacific ocean, another natural phenomenon called the North Atlantic oscillation causes variability in local climates in the Northern Hemisphere. During the winters of 2010 and 2011, this oscillation exhibited an unusual and persistent pattern that caused cold air from the Arctic to move down to the United States and Europe, while warm air traveled up to the Arctic. This made it so that while much of North America and Europe was unusually cold, the Arctic was, in fact, much warmer during the winter. Even now, the total area of Arctic sea ice is near record lows this year.

In contrast, the extremely hot weather in the rest of the Northern Hemisphere cannot be explained by natural variations in climate, but require an outside explanation. This paper demonstrates that while there may be locally extreme cold events in weather than run counter to the overall trend of anthropogenic climate change, the overall trend for the entire planet is warming.