Studentsmart.in - Eco Club Articles

Science and Policy News will strive to present or direct you to the timeliest social, scientific, and logistic information available on the global warming issue.

Researchers Find Evidence of Human-Produced Warming in Oceans

A new study has found a “compelling agreement” between observed changes in ocean temperatures since 1960 and the changes simulated by two climate models under rising atmospheric concentrations of greenhouse gases. In all of the world’s ocean basins, the warming predicted by the models for the upper 700 meters (2,300 feet) of the ocean corresponded to actual measurements obtained at sea, with confidence exceeding 95 percent.

“The immediate conclusion is that human influences are largely responsible for the warming signal,” the authors write. “The statistical significance of these results is far too strong to be merely dismissed, and should wipe out much of the uncertainty about the reality of global warming,” said lead author Tim Barnett of the Scripps Institution of Oceanography.

Barnett and his colleagues used one of the models to explore whether the climate’s own natural variability could account for the warming oceans, or whether the warming could be explained by other natural factors such as solar variability and volcanic eruptions. In neither case could the model replicate the warming that has been observed in the real world. The changes were simply too strong to be explained by natural causes.

The authors argue that since these two climate models have been shown to simulate past changes accurately, their predictions for future changes, at least out to the next 20-30 years, “are apt to be reasonably good.” The study was published in the June 2, 2005 online version of the journal Science.

Precise measurements of temperature within the ocean confirm that the Earth is absorbing more energy from sunlight than it emits back to space, providing perhaps the strongest evidence to date that rising concentrations of greenhouse gases and other pollutants are the primary cause of the current global warming trend. The findings are reported in the April 28, 2005 issue of the journal Science.

“The magnitude of the imbalance agrees with what we calculated using known climate forcing agents, which are dominated by increasing human-made greenhouse gases,” said lead author James Hansen, director of the NASA Goddard Institute for Space Studies.

The average energy imbalance amounts to 0.85 + 0.15 Watts per square meter, largely reflecting the amount of heat soaked up and stored by the world’s oceans. The imbalance implies that the global temperature takes decades to fully respond to changes in greenhouse gases, because the ocean’s thermal inertia acts as a brake on warming. It also implies that the Earth would warm by about 1 degree Fahrenheit over the course of the current century even if greenhouse gas concentrations were held constant at today’s levels, because the oceans will continue to absorb energy, increase in temperature, and warm the atmosphere until the energy coming in from the sun and the energy emitted out to space are in balance. In addition, the new findings imply that sea level rise and the disintegration of ice sheets are likely to increase.

The authors note that the increasing heat storage in the ocean cannot be explained by natural fluctuations. Under natural conditions, the ocean would release its heat more slowly only if its surface cools (if, for example, cool water from the ocean depths rose to the surface). But the ocean’s surface has been warming, suggesting that the warming climate is the more viable explanation for the phenomenon.

Doubling the concentration of carbon dioxide in the atmosphere could cause the Earth to warm by less than 2ºC (3.6ºF) or more than 11ºC (19.8ºF), according to a new study based on more than 2,500 climate model simulations carried out on thousands of personal computers. The study, by a team of British scientists, aimed to determine the full range of the climate’s sensitivity (the amount by which the global temperature changes in response to a given increase in greenhouse gases) by testing multiple versions of the same climate model. Each version differed from the others in several ways, allowing the researchers to explore the effects of a range of uncertainties in how the model represents the atmosphere.

The sensitivities in the different versions ranged from less than 2ºC to more than 11ºC, more than twice the 2-5ºC range estimated by the Intergovernmental Panel on Climate Change in its most recent assessments. Both the low end and the high end of the new range should be considered plausible, the researchers say, because the model versions that produced those sensitivities also produced realistic simulations of past climate.

The new findings come from the world’s largest climate modeling experiment, climateprediction.net, which runs models on thousands of personal computers. More than 95,000 people from 150 countries participate in the project, including more than 24,000 in the United States. The software incorporating the climate model runs in the background when the computer is idle.

Did global warming cause the devastating European heat wave of 2003? It’s a question that’s impossible to answer, because extreme weather events can occur randomly under any climatic conditions. But a team of British scientists has developed a way to estimate the extent to which human-induced climate change affects the probability that a heat wave might occur in today’s climate. Their conclusion: climate change has at least doubled the risk of a major heat wave in continental Europe.

Peter Stott of the UK Met Office’s Hadley Center for Climate Prediction and Research and colleagues compared two sets of simulated European summer temperatures from a climate model, one set that incorporated the effect of human contributors to climate change (greenhouse gases and sulfate aerosols) and another that accounted only for natural influences on climate. They then calculated the change in risk of extreme heat waves that can be attributed to the increase in greenhouse gases.

Stott and his colleagues compared the model’s simulations with actual observed climate records to ensure that it accurately portrayed the natural variability of European summers, and their analysis allowed for uncertainties in the nature and extent of human-induced climate change. The authors, who report on their findings in the 2 December 2004 issue of Nature (vol. 432, pp. 610-614), note that a summer as hot as that of 2003 might actually be classed as anomalously cold by the end of this century, if model projections turn out to be accurate.

Researchers estimate that the summer of 2003 was the hottest in Europe since at least the year 1500, leading to 22,000-35,000 heat-related deaths across the continent and more than $12 billion in crop losses.

The Arctic is warming nearly twice as rapidly as the rest of the globe, according to the final report of the Arctic Climate Impact Assessment, a four-year study conducted by an international team of 300 scientists. In Alaska, Western Canada, and Eastern Russia, average winter temperatures have increased as much as 3-4C (4 to 7F) in the past 50 years. Snow cover extent has declined by about 10 percent during the past 30 years, and permafrost has warmed by up to 2C (3.6F) in recent decades. The average extent of sea-ice has declined by 15-20 percent over the past 30 years.

“The Arctic is experiencing some of the most rapid and severe climate change on Earth,” says Robert Corell, chair of the assessment. “The impacts of climate change on the region and the globe are projected to increase substantially in the years to come.”

Based on a mid-range estimate of future emissions of greenhouse gases and projections from models used by the Intergovernmental Panel on Climate Change, the assessment projects that at least half the summer sea ice in the Arctic will melt by the end of this century, along with a significant portion of the Greenland Ice Sheet. The region overall is projected to warm an additional 4-7 C (7 to 13 F) by 2100.

These changes would contribute to global sea-level rise and would intensify global warming through a variety of feedback mechanisms. They also are expected to threaten the survival of some arctic animal species, such as polar bears and some seals, and would present many challenges to the health and food security of indigenous cultures. Reductions in sea ice would facilitate marine transport and access to resources in the region, with transarctic shipping becoming feasible during the summer months within several decades.

The Northern Hemisphere’s climate during the past 1,000 years may have been much more variable than suggested by recent analyses of tree-rings, ice cores, and other indirect sources of data on past temperatures. A new study suggests that the statistical method used in previous reconstructions of past climate is flawed, because it underestimates—perhaps by a factor of two or more—fluctuations in temperature that occurred over decades or centuries.

Hans von Storch of the GKSS Research Center (Geesthacht, Germany) and colleagues tested the ability of this statistical method to reproduce known temperature changes in the “virtual world” of a climate model. The researchers first used the model to produce a simulated temperature record for the past 1,000 years. They then generated virtual data for tree rings, ice cores, and other indirect data sources by adding statistical noise to the model’s simulated temperatures, mimicking the noise inherent in real-world data (such as the influence of changes in moisture and pest outbreaks on the width of tree rings). The team then applied the statistical method used in previous analyses to see how accurately it could reproduce the model’s simulated temperature record from the virtual tree ring and ice core data. They found good agreement for the past 100 years or so, but large disparities over longer timescales.

The new findings raise the possibility that the current warming trend may not be as unusual or unprecedented as previously thought, and that the climate’s natural variability may be greater than most recent studies have assumed. However, the authors emphasize that their results do not challenge conclusions that rising concentrations of greenhouse gases have contributed to the warming of the 20th century.

A comprehensive new computer modeling study suggests that hurricanes will become more intense as the climate warms, with stronger winds and heavier rainfall. The study projects an average 6 percent increase in maximum hurricane winds by the year 2080, along with an 18 percent increase in the rate of precipitation within 60 miles (100 kilometers) of the storm’s core. The increase in intensity amounts to roughly a half step in the 5-category hurricane scale. These specific projections are based on the assumption that carbon dioxide concentrations in the atmosphere will increase by 1 percent per year (compounded) over the next 80 years, which is higher than the current rate of about 0.6 to 0.7 percent per year.

The study’s authors do not expect the changes in hurricane intensity to be detectable “for decades to come,” but warn that there may be a gradually increasing risk of highly destructive category 5 storms over the course of this century.

The study’s basic findings are consistent across nine different climate models and a range of characterizations of physical processes in a hurricane model, bolstering the conclusions. Previous studies based on input from one climate model had also shown a tendency toward stronger hurricanes in warmer climates, but it was unclear how much of this effect was due to assumptions in the model.

Two teams of researchers have provided conclusive evidence that Antarctic ice shelves can act as “brakes” on the land-based glaciers behind them, slowing their flow toward the sea. When the ice shelves collapse, the glaciers surge forward, dumping more ice into the ocean.

The breakup of ice shelves does not contribute directly to sea level rise, because the ice shelves are already floating on water. But the new findings indicate that the collapse of ice shelves may lead to higher sea levels by allowing the flow of glaciers to accelerate.

When the Larsen B ice shelf collapsed in 2002, researchers observed nearby glaciers flowing up to eight times faster than they did prior to the breakup. The research teams used RADARSAT and Landsat measurements to monitor changes in the glaciers’ rate of flow. Three of the glaciers behind the collapsed ice shelf flowed eight times faster in 2003 than they did in 2000, slowing moderately in late 2003. Two glaciers increased their rate of flow by a factor of two in early 2003 and by a factor of three by the end of 2003, compared with their flow in 2000. Nearby glaciers in areas where the ice shelf remained intact showed no significant changes. The glaciers in the Larsen area are not large enough to have a noticeable effect on sea level rise, but glaciers to the south are much bigger and could affect sea levels if nearby ice sheets were to collapse.

The findings are reported in the September 22, 2004 issue of Geophysical Research Letters.

A new climate modeling study projects that heat waves in North America and Europe will become more intense, more frequent, and longer lasting in the decades ahead. In the United States, the increase in the severity of heat waves will be greatest in the West and the South.

In their model, Gerald Meehl and Claudia Tebaldi of the National Center for Atmospheric Research found that an increase in the atmospheric concentration of greenhouse gases intensifies an atmospheric circulation pattern that researchers have observed during past heat waves in Europe and North America. As the pattern becomes more pronounced, severe heat waves occur in the Mediterranean region and the southern and western United States.