Archive for the ‘climate change science’ Category
« Older Entries |More on natural variability vs. anthropogenic warming
Thursday, March 11th, 2010
Matthew McDermot features another GRL article that comes to a similar conclusion as the last post: The kinds of natural variability we have experienced in volcanoes and solar cycles over the past 1000 years has been relatively small compared to the temperature changes we face with anthropogenic greenhouse gases.
This paper by Thomas Crowley is an earlier example of how climate scientists compare the relative effects of natural vs. human factors on climate over the past 1000 years.
Posted in climate change science | 1 Comment »
Natural climate factors unlikely to put the brakes on greenhouse-gas-driven sea level rise this century
Wednesday, March 10th, 2010
The IPCC 2007 report projected a conservative sea level rise of about 18-59 cm by the year 2100.
Why conservative? Because it mainly accounted for things we know are happening and can measure well—like thermal expansion of the ocean and melting of land glaciers (see here for a discussion of the Kilimanjaro example). What it doesn’t do so well is account for all of the potential ways that the big ice sheets (Greenland and Antarctica) can contribute to sea level rise. Things like ice flow and mass loss are generally assumed to be constant, even though recent research papers discussed in previous posts (here and here) suggest they are accelerating.
Since the publication of the IPCC report in 2007, there have been several studies suggesting that sea level rise will be 1-2 meters or more by 2100 (one example here). One study looked at geological evidence for sea level rise during the previous interglacial period 125,000 years ago, which was 1-2 degrees C warmer than today. Their work indicated that there was a 95% chance that sea level rose by 6 meters (22 feet).
In a forthcoming issue of Geophysical Research Letters, Svetlana Jevrejeva and colleagues used statistical models to project sea level rise by 2100.1 But they also did something else interesting. They looked back several thousands of years to the most extreme events that could cause climate cooling—things like severe volcanic eruptions, which create stratospheric dust clouds that block sunlight.
If events like this were to happen again, they asked, would they cause enough cooling to be able to slow sea level rise caused by greenhouse gases?
The answer is no. There appears to be no natural factors like vulcanism that will significantly slow greenhouse-gas-driven sea level rise that we are already committed to or future sea level rise that we may experience if we continue to emit fossil fuels.
Excerpts (emphasis mine):
- With the assumption that sea level will continue to respond over the next 100 years to the same forcings that have influenced it during the past 1000 years, we estimate 0.6 -1.6 m of global sea level rise in the 21st century using a statistical model driven by projected natural and anthropogenic forcings.
- In contrast to the 20th century sea level rise that was associated with a significant contribution of 25% from natural (solar and volcanic) forcing, 21st century sea level rise will be clearly dominated by the changes in CO2 and other greenhouse gases.
- Alternative scenarios for solar forcing with a potential decrease in solar irradiance of 1W/m2 (using the lowest level recorded throughout the last 9300 years) only produce a 10-20 cm reduction in our estimate of 21st century sea level rise.
- If we utilize the 13th century past volcanic forcing to estimate a possible (but unlikely) contribution from volcanic activity, then an almost negligible 8 cm decrease is projected in the estimated sea level rise.
- The suggested reduction of radiative forcing by injections of SO2 into atmosphere (equivalent to a Pinatubo eruption every 4 years) would be equivalent to delaying sea level rise by 12 -20 years.
- A “no changes in radiative forcing” scenario produced 16-22 cm (with lower limit of 10 cm and upper limit of 31 cm) sea level rise in the 21 century due to the inertia of the climate system, providing evidence that conditions established during the past centuries have already committed us to a considerable global sea level rise during the next 100 years.
1Jevrejeva, S., J. C. Moore, and A. Grinsted (2010). How will sea level respond to changes in natural and anthropogenic forcings by 2100? Geophysical Research Letters : 10.1029/2010GL042947
UPDATE: RealClimate provides more explanation of the IPCC being too cautious about sea level rise.
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Photo Credit: http://www.flickr.com/photos/gsfc/ / CC BY 2.0
Posted in climate adaptation, climate change science, polar ice, sea level rise | No Comments »
How much is a ton of CO2?
Tuesday, March 9th, 2010
One of the challenges of climate literacy is helping folks visualize fossil fuel emissions and their impacts.
Last year, Bowdoin College completed its emissions inventory and climate action plan. We discovered that the campus emits a total of 24,000 tons of CO2 equivalents each year. So how much is that really?
One student decided to help illustrate this by creating an art installation, cordoning off a 27-ft x 27-ft x 27-ft cube in the student center with red ribbon.
Now imagine 24,000 of these cubes emanating from a college campus each year. That helps show the magnitude of the challenge.
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Photo courtesy of Bowdoin College
Posted in behavior, campus sustainability, climate change science, communication and framing, energy, higher education | 1 Comment »
The hidden global CO2 emissions of consumerism
Monday, March 8th, 2010
It’s been easy for citizens of the developed, industrialized world to criticize China and India over their rapidly growing greenhouse gas emissions. This was one of the major reasons why the Kyoto Protocol was never ratified in the United States.
As many have pointed out, however, there are several flaws with this argument:
- The per-capita carbon emissions in China and India remain much lower (1/4 and 1/16, respectively) compared to the U.S..
- Perhaps more importantly, some of the carbon emission in these countries is caused by the production of export goods to fuel consumer demand in wealthy nations. Thus, we are responsible for “shadow carbon emissions” that get attributed to developing nations.
Until today, there haven’t been very good estimates of these kinds of shadow emissions.
In the Early Edition of the Proceedings of the National Academy of Sciences, Steven Davies and Ken Caldeira examine how much CO2 is embodied in the import and export of goods.1
Their results are interesting (excerpts below—If you can get a copy of the article, check out figures 1 and 2; they are terrific visuals for this information. Alas, copyrights don’t allow me to post them):
- Approximately 6.2 gigatonnes (Gt) of CO2, 23% of all CO2 emissions from fossil-fuel burning, were emitted during the production of goods that were ultimately consumed in a different country.
- Emissions imported to the United States exceed those of any other country or region, primarily embodied in machinery (91 Mt), electronics (77 Mt), motor vehicles and parts (75 Mt), chemical, rubber, and plastic products (52 Mt), unclassified manufactured products (52 Mt), wearing apparel (42 Mt), and intermediate goods (654 Mt).
- These imports are offset by considerable US exports of transport services (49 Mt CO2), machinery (42 Mt), electronics (26 Mt), chemical, rubber, and plastics products (25 Mt), motor vehicles (22 Mt), and intermediate goods (263 Mt).
- [G]oods imported to Western Europe and Japan embody much more CO2 per US$ than do their exports, reflecting the import of energy-intensive products from elsewhere.
- The carbon intensity of imports to China, Russia, India, and the Middle East is consistently far less than that of their exports.
- China is by far the largest net exporter of emissions, followed by Russia, the Middle East, South Africa, Ukraine, and India and, to a lesser extent, Southeast Asia, Eastern Europe, and areas of South America.
- The primary net importers of emissions are the United States, Japan, the United Kingdom, Germany, France, and Italy. Although the overall mass of emissions is much less, the other countries of Western Europe are all net importers, as are New Zealand, Mexico, Singapore, and many areas of Africa and South America. Similarly, Canada, Australia, Indonesia, the Czech Republic, and Egypt are among the countries whose net exports of emissions are small.
- On a per-capita basis, net imports of emissions to the United States, Japan, and countries in Western Europe are disproportionately large, with each individual consumer associated with 2.4–10.3 tons of CO2 emitted elsewhere.
Their conclusion:
Consumption-based accounting reveals that substantial CO2 emissions are traded internationally and therefore not included in traditional production-based national emissions inventories. The net effect of trade is the export of emissions from China and other emerging markets to consumers in the United States, Japan, and Western Europe. In the large economies of Western Europe, net imported emissions are 20–50% of consumption emissions; the net imported emissions fall to 17.8% and 10.8% in Japan and the United States, respectively. In contrast, net exports represent 22.5% of emissions produced in China. Thus, to the extent that constraints on emissions in developing countries are the major impediment to effective international climate policy, allocating responsibility for some portion of these emissions to final consumers elsewhere may represent an opportunity for compromise.
1Steven J. Davis and Ken Caldeira (2010). Consumption-based accounting of CO2 emissions PNAS : 10.1073/pnas.0906974107
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Photo Credit: http://www.flickr.com/photos/deks/ / CC BY-NC 2.0
Tags: China, India
Posted in behavior, climate change science, climate economics, energy, nature and culture, technology, transportation | 1 Comment »
East Siberian Arctic Ocean discovered to be venting a lot of methane
Thursday, March 4th, 2010
Methane (CH4) release from ocean sediments has long intrigued scientists. There is an event that happened 54 million years ago called the Paleocene-Eocene Thermal Maximum (PETM), when 3,000-4,500 gigatons of carbon were released from the oceans, possibly as large methane burps caused by underwater landslides.
That’s a lot of carbon—more than 10 times the total amount we have burned as fossil fuels since the Industrial Revolution began. Researchers think that it could have caused ocean temperatures to rise by as much as 5 degrees C and the atmosphere to warm by 5-9 degrees C. And when all of that methane carbon in the atmosphere oxidized to CO2, it dissolved back into the ocean and it reacted with water to form a weak acid
H2O + CO2 –> H2CO3 (carbonic acid)
which caused the ocean to acidify, melting the calcium carbonate shells of marine organisms and leading to one of the largest known marine extinction events of all time.
A new study by Natalia Shakhova and colleagues1 in this week’s issue of Science indicates that the coastal marine shelf in eastern Siberia may now be venting as much methane as was previously thought for all of Earth’s oceans combined.
In their words:
These findings do change our view of the vulnerability of the large sub-sea permafrost carbon reservoir on the [East Siberian Arctic Shelf] ESAS; the permafrost “lid” is clearly perforated, and sedimentary CH4 is escaping to the atmosphere.
For a cool visual of what methane release from ocean sediments looks like, check out the images in this article at Science Daily.
Whether or not the thawing of sub-sea permafrost will release enough methane to cause another PETM-type warming/extinction event is an active area of investigation. Nobody knows for sure yet. There is a lot of uncertainty in determining the size of the frozen methane pool in global marine sediments (possibly 500 – 2,500 gigatons of carbon), and the potential rate of release with warming is poorly known. Clearly, there’s more work to do.
Even if the methane release is not as catastrophic as a PETM-type event, accelerated release will likely lead to a positive feedback on current warming, meaning that all associated impacts will happen faster than originally expected. As I’ve said before, that becomes a nightmare scenario for policy makers.
1Shakhova, N., Semiletov, I., Salyuk, A., Yusupov, V., Kosmach, D., & Gustafsson, O. (2010). Extensive Methane Venting to the Atmosphere from Sediments of the East Siberian Arctic Shelf Science, 327 (5970), 1246-1250 DOI: 10.1126/science.1182221
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Posted in climate change science | 1 Comment »
Al Gore weighs in on the state of climate change
Saturday, February 27th, 2010
…in an op-ed piece in today’s NY Times.
Excerpts (links his):
[T]he scientific enterprise will never be completely free of mistakes. What is important is that the overwhelming consensus on global warming remains unchanged. It is also worth noting that the panel’s scientists — acting in good faith on the best information then available to them — probably underestimated the range of sea-level rise in this century, the speed with which the Arctic ice cap is disappearing and the speed with which some of the large glacial flows in Antarctica and Greenland are melting and racing to the sea.
Because these and other effects of global warming are distributed globally, they are difficult to identify and interpret in any particular location. For example, January was seen as unusually cold in much of the United States. Yet from a global perspective, it was the second-hottest January since surface temperatures were first measured 130 years ago.
Similarly, even though climate deniers have speciously argued for several years that there has been no warming in the last decade, scientists confirmed last month that the last 10 years were the hottest decade since modern records have been kept.
The heavy snowfalls this month have been used as fodder for ridicule by those who argue that global warming is a myth, yet scientists have long pointed out that warmer global temperatures have been increasing the rate of evaporation from the oceans, putting significantly more moisture into the atmosphere — thus causing heavier downfalls of both rain and snow in particular regions, including the Northeastern United States. Just as it’s important not to miss the forest for the trees, neither should we miss the climate for the snowstorm.
….The political paralysis that is now so painfully evident in Washington has thus far prevented action by the Senate — not only on climate and energy legislation, but also on health care reform, financial regulatory reform and a host of other pressing issues.
….Some analysts attribute the failure to an inherent flaw in the design of the chosen solution — arguing that a cap-and-trade approach is too unwieldy and difficult to put in place. Moreover, these critics add, the financial crisis that began in 2008 shook the world’s confidence in the use of any market-based solution.
But there are two big problems with this critique: First, there is no readily apparent alternative that would be any easier politically….Second, we should have no illusions about the difficulty and the time needed to convince the rest of the world to adopt a completely new approach.
Updates: There is a wide range of opinion on the IPCC these days:
- Union of Concerned Scientists weighs in on climate warming and the criticism of the IPCC.
- Roger Pielke, Jr. has been writing a lot about the IPCC recently (here, here, here)
- Joe Romm at Climate Progress
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Tags: Al Gore
Posted in climate change science, climate economics, climate skeptics deniers and contrarians, communication and framing, energy, policy, sustainability | No Comments »
Can “tree sweating” buffer Europe against future heat waves?
Wednesday, February 24th, 2010
Trees can have a big impact on climate in many ways, as we have been tracking over the past few weeks here at Global Change.
Changes in species ranges, such as the shift of boreal forests northwards into barren-ground tundra, can lower albedo (reflectivity) in winter, thereby warming regional climate.
Last week, we also saw how trees can act as methane chimneys that release this greenhouse gas produced in swampy soils.
In another study, we saw that rising CO2 in the atmosphere can cause forests to grow faster such that they become nutrient starved—especially by soil nitrogen. This causes tree growth to slow. Unfortunately, we saw that most models of climate change (which assume forests are removing CO2 from the atmosphere) don’t take nutrient limitation into account, so scientists are expecting forests to soak up more CO2 than they probably will. This means that atmospheric CO2 rise (and warming) will likely be worse than expected—maybe by as much as 0.5 degree by 2050 and 1 degree by the year 2100.
A further study indicated that increased deciduous forests in the Arctic can increase transpiration (water flow from soils to the atmosphere through plants). This extra water vapor in the atmosphere might act as a greenhouse gas and cause climate in high latitudes to warm by an extra 1 degree C.
In the OnlineFirst issue of Climatic Change (this article is open access), Su-Jong Jeong and colleagues explore other possible forest impacts on climate.1
Specifically, they focused on heat waves in Europe and asked whether forests might be able to help alleviate the impacts of them.
Here’s the idea: In a warmer world with more CO2, forests grow more and there is higher leaf area. This leads to more transpiration. When plant leaves lose water, this acts to cool the plants a lot like sweating does in animals (because the transition of less-energetic liquid water to more-energetic water vapor requires heat input, which comes from the plant). This results in cooler trees and cooler landscapes. Subsequent rainfall from all of this water vapor could supposedly cool landscapes further.
These authors argue that this mechanism can actually cause forested regions in Europe to cool by 1 degree C, thereby potentially lessening the impacts of future heat waves.
Wait a minute, you might be asking, I thought you said that transpiration causes climate to warm? That’s a good point, so let me try to clarify. In the Arctic example above, the researchers were focusing on water vapor as a potential greenhouse gas in the atmosphere. In the Jeong article here, they are focusing on the effects of water evaporation on the temperature of tree leaves at the surface of the earth.
It’s an interesting idea that’s not particularly new. However, there are several potential challenges with the Jeong article that I didn’t see addressed:
- When the water vapor from trees condenses into liquid clouds and rain, this process gives off heat (because we are going from a more energetic gaseous form to a less energetic liquid form). This warms the atmosphere wherever condensation happens, which presumably would also be Europe.
- If increased transpiration is a general feature of European forests in a warmer world, and water vapor remains persistently high in the atmosphere, it can act as a greenhouse gas like the Arctic paper above suggests. This, too, will warm rather than cool climate.
- And, finally, heat waves are often accompanied by droughts when transpiration is generally low because trees are water stressed. This diminishes the cooling effect and can actually cause landscapes to warm as tree leaves warm up and release heat rather than water vapor.
1Jeong, S.J et al (in press) Potential impact of vegetation feedback on European heat waves in a 2 x CO2 climate. Climatic Change
DOI 10.1007/s10584-010-9808-7
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Tags: heat wave, trees and forests
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Global change is causing forests to grow more
Wednesday, February 3rd, 2010
Decades of research have shown that increasing carbon dioxide in the atmosphere can cause trees to grow better. However, what we don’t know as well is how much rising temperatures and CO2 impact forest growth over longer time scales, such as the entire 20th century.
This is a harder question to answer for one big reason: When you look back that long, you have to rely on things like tree rings to measure growth rate. This also means you have to contend with natural regeneration cycle of individual trees. Young trees often grow fast, and growth slows as the trees get older. If you cut down a tree and look at a cross section of tree rings, you can often see wide rings fading to narrow rings over the lifespan of an individual.
In a forthcoming article1 in the Proceedings of the National Academy of Sciences (open access), Sean McMahon and colleagues investigated the question of long-term forest response to global change in Maryland forests.
Using statistical techniques, they were able to factor out the messiness of these aging trends to look for effects caused mainly by a changing physical environment.
They found that 80% of the trees grew more than you would expect by stand-level growth dynamics alone. However, they found it difficult to pin this trend on any single environmental factor, concluding that temperature, increased lengths of growing seasons, and increased CO2 were likely synergistic drivers.
This is an interesting result because it contrasts with the results of elevated CO2 experiments, which show that forest growth typically slows a few years after trees are subjected to experimentally raised CO2. What those studies are finding is that nitrogen in soils could become limiting and essentially shut off extra growth caused by CO2 fertilization.
The implications are fairly significant: Either the Maryland site is unusually nutrient rich, and we have to discount the ability to generalize from that one study, or the elevated CO2 experiments may not fully capture the dynamics of how forests responding to climate change. This should spur an interesting debate.
1McMahon, S.M. (in press) Evidence for a recent increase in forest growth. Proceedings of the National Academy of Sciences
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Posted in climate change science | 2 Comments »
Trees: Another way to increase global methane?
Monday, February 1st, 2010
Methane is a potent greenhouse gas. Unlike CO2, which is produced by the aerobic (in the presence of oxygen) breakdown of organic matter, methane is produced by the breakdown of organic matter in anaerobic environments, such as livestock rumens, wetland soils, landfills, and rice paddies.
When we think of methane production, we don’t usually think about trees, but it looks like they may facilitate methane to the atmosphere. How, you might ask, since most trees live in well-aerated soils?
In a forthcoming article1 in Geophysical Research Letters, Andrew Rice and colleagues show that trees in lowland, swampy areas actually conduct methane produced in soils up their stems and out their leaves, making trees an effective methane chimney.
We’ve known for years that marsh and bog plants do this, but nobody’s really looked at trees before. The trees themselves are not making the methane (that’s done by soil bacteria), but they appear to do two things that increase the overall flux (movement) of methane to the atmosphere: (1) tree stems provide a quick methane escape route from soils to the atmosphere and (2) trees leak root exudates (small organic molecules), which could be an organic carbon source for microbes that make methane.
In this study, they put bags around aboveground tree biomass to catch and measure methane, so it’s clear that #1 happens. However, #2 needs further study. You could measure it by dosing a tree with radiocarbon (14CO2) and then seeing if that gets turned into sugars by photosynthesis and eventually leaked out of roots, ultimately turning into 14C methane (14CH4) that is transported up the tree stems.
How much methane? About 60 teragrams (1012g), or about 10% of the global production each year. Big enough to pay attention to.
1Rice, A.L. et al. (in press) Emissions of anaerobically produced methane by trees. Geophysical Research Letters.
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Tags: trees and forests
Posted in climate change science | 1 Comment »
Can we alter climate by installing white roofs?
Monday, January 11th, 2010
When reviewing the most popular words of 2009, I was surprised to see that “albedo” didn’t crack the top 5—Tweet, Obama, H1N1, Stimulus, and Vampire. I bet you were equally shocked.
Albedo is a simple concept—the reflectivity of a landscape—but it’s hugely important in understanding how the surface of the Earth impacts climate. As we saw in a recent post, things like thawing sea ice, northward advancing treeline, and asphalt paving all darken landscapes, causing more solar radiation to be absorbed and temperatures to climb—one of the reasons for the so-called urban heat island effect.
So what would happen if we were to install white roofs? In a forthcoming article1 in Geophysical Research Letters (subscription required), Keith Oleson and colleagues use biophysical models to address this.
Their answer: White roofs reflect more sunlight and cool buildings. Averaged over all urban areas in the world, the urban heat island effect declines by 33%, causing maximum and minimum daily temperatures to decrease by 0.6 and 0.3 degrees C, respectively.
At face value, this sounds great. But, there’s a potential hidden cost of cool buildings—heating. Interestingly, they found that white roofs caused space heating to increase more than air conditioner use declined, suggesting that energy use might actually increase with white roofs!
1Oleson, K. et al. (in press) The effects of white roofs on urban temperature in a global climate model. Geophysical Research Letters.
Related post: New ideas about how changing vegetation at high latitudes can cause climate warming to accelerate
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Tags: albedo
Posted in behavior, climate adaptation, climate change science, energy, solutions, sustainability, technology | No Comments »
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