The International Panel on Climate Change, composed of over 3,000 scientists, last year released its third global assessment report, stating that there is “likelihood” that human activity is the reason for the earth’s increasing climate change.
Professor Adil Najam, a member of the IPCC and a faculty member at the BU Center for Energy and Environmental Studies, agrees that carbon dioxide has measurable climate effects: “There is a robust and clear relationship between the increase of the use of carbon-based fossil fuels and global climate change … carbon dioxide and other greenhouse gases can be triggers of climate change.”
Najam says global warming is no longer disputed among scientists.
“The scientific assessment is pretty clear. Human-induced global warming is a real process, and although there are debates — even important ones — about the extent and mechanism of it, no one questions whether or not it is happening.”
Carbon dioxide, produced from the burning of fossil fuels, acts as a selective filter in the atmosphere by allowing solar radiation through to the earth. The gas then blocks heat coming off the earth from escaping into space, warming the atmosphere.
A study recently undertaken by an international team of scientists and three Boston University researchers uses satellite imagery to gain perspective on the role that forests play in the interactions between human activity, carbon and climate change.
A carbon sink is a geographical area that stores large amounts of carbon. Since trees absorb carbon dioxide from the atmosphere during photosynthesis, they are natural carbon sinks.
Carbon sinks have attracted attention as a way to counteract the affects of human-produced carbon dioxide on the global climate. However, the vast tracks of northern forest are largely inaccessible to researchers trying to measure carbon absorption rates.
The authors of the study used satellite imagery obtained from the National Oceanic and Atmospheric Administration to observe the changing levels of greenness in forests for the period from 1981-99. Greenness is the measure of the rate of photosynthesis, and therefore of the amount of carbon trees take into their tissues. This analysis was then compared to ground-based measurement techniques to ensure that the new method was accurate.
“Satellite images of the planet have been accumulating in the last 20 years,” says Robert Kaufmann, College of Arts and Sciences associate professor of geography and one of the study’s nine authors. “This allows us to do something we never could before: watch what was happening on a global scale.”
The study, “A Large Carbon Sink in the Woody Biomass of Northern forests”, was the first use of remote sensing to measure the biomass of forests. Before the application of satellite technology, ground-based inventories of forest density and size were needed to gather such information. Researchers would travel to forest sites and measure variables like average height and width of trees and the carbon content of a few sample trees.
However, vast tracts of forest in North America, Russia and northern Europe were inaccessible to researchers. The study authors analyzed carbon-absorption data collected between 1981 and 1999 using these ground techniques and compared them to changes in forest greenness shown in satellite images. Since changes in greenness correlate to changes in biomass, they were then able to develop an equation to establish the relationship between greenness and carbon dioxide absorption.
The application of this equation allowed them to extrapolate the amount of carbon dioxide absorbed annually over the study period for every eight square kilometer area of land north of the 30th parallel, nearly 3.7 billion square kilometers of forest. The 30th parallel passes through the southern edge of the United States.
“Right now, we can’t balance the global carbon cycle,” Kaufmann says. “We put it into the atmosphere when we burn fossil fuels and cut down trees, and although the ocean takes some of it out, the carbon we put into the atmosphere is going somewhere. We think we can account for this missing carbon by looking at the amounts plants and trees are taking it up.”
Accurate description and measurement of terrestrial carbon sinks is crucial to developing environmental policies. The Kyoto Protocol, a treaty prepared by the United Nations to reduce global greenhouse gas emissions, would offer credit to those countries that cultivate forests specifically as carbon sinks.
“It is not clear how much of an effect the Kyoto treaty would have, since it only restricts emissions to 1990 levels,” Kaufmann says. “This merely slows the rate at which the world warms.”
“I think it [the Kyoto Protocol] is insufficient, but I strongly believe that it is an important step in the right direction. It’s a beginning,” Najam says. “Even if every country signed on, it would not make a big dent in the problem. Better solutions are available, and the government could take advantage of them. These ‘no-regret’ solutions have benefits even if they are found to have no effects on slowing of stopping climate change. Planting trees, developing — and driving — more efficient cars, these are things we can do now without a treaty.”
The results of the study show that forests in northern Europe, Russia and the United States have been increasing the amounts of carbon stored. The authors suggest this pattern is possibly due to improved fire control practices in the US, declining forests harvests in Russia, improved forest management techniques in the Nordic countries and — ironically — longer growing seasons due to warming in all these areas.
Forests in Canada showed a decrease in the amount of carbon absorbed and stored annually, possibly because of increased fire incidence decreasing the size of forests and fungal and insect infestations slowing the growth of trees. Slower growing trees absorb less carbon than more quickly growing ones.
This study provides a way to measure how land areas absorb carbon that human activity places in the atmosphere. However, it does not offer information on how carbon emissions are effecting climate change or how humans can prevent pushing the climate into such severe change that lives are put at risk.
“I think people should be concerned, absolutely,” Kaufmann says. “One of the key statistics that everyone should keep in mind is that the earth was only 3-4 degrees cooler in the last ice age.”
Najam puts that seemingly small temperature change in perspective.
“In Boston, the temperature might change by 6 degrees on any given day, and that doesn’t kill us. But, to understand what the effects of climate change are you need to understand the difference between weather and climate: weather is the state of the atmosphere at a moment in time, but climate is climate is over time, over decades and centuries.
“A fluctuation in the weather of 10 degrees is inconsequential, but with a change in climate of 1 degree, the effects are profound. I can explain it like this; if you go out in the freezing cold without your sweater for a moment, you shiver a little but are not harmed, but if you sit there for two days, you are going to get pneumonia.
“Like our body, nature can handle weather changes, but it is very difficult to withstand and then recover from long-term climate changes that will trigger other far-reaching changes. And people certainly could easily withstand such change: it changes the crop balance, it would require changes in city infrastructures since places will get snow where snow never fell.
“The issue here is whether or not human-induced global warming in the last 200 years or so across the globe has messed up the global warming-cooling cycle to the extent that the damage might be irreversible,” Najam says.
President Bush has not decided to join the other nations in the international community by agreeing to follow the regulations of the Kyoto Protocol. The Clean Air Act of 1990, the most recent government attempt to address the problem of emissions and climate change, does not recognize carbon dioxide as a pollutant.
The study was published in the December 18 issue of the Proceedings of the National Academy of Sciences, and is available online at www.pnas.org.
“If we are going to do something seriously about climate change, it will be very expensive,” Najam says. “Whoever must deal with the price will downplay the fact of climate change so as to avoid the issue. That is of course the tough question of policy change: the cost of doing something must be borne by people today, but the benefits will affect only those who come generations later.”
Carbon sinks accept only a limited amount of carbon each year, rather than acting as scrubbers that constantly remove clean the air.
“Forests might provide a temporary respite, but they are only a temporary solution,” Najam says. “You cannot forest the whole planet, and even if you could, it would not have the capacity to absorb all the carbon we are producing.”
The land and oceans absorb about 3.4-4 billion tons of carbon dioxide each year, half of the amount produced by emissions and forest destruction.
Najam suggests that the best solution to stem the effects of human activity on the global climate is one that can be done by anyone.
“There is only one solution: we must drastically reduce our carbon dioxide emissions. It will be solved only by meaningful changes in lifestyle. In some ways your average undergraduate is the best person to do something about this. If enough people are willing to make small changes, it takes surprisingly little to make a difference.”
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