More Evidence Accumulates of Record Greenhouse Gases and Warming Temperatures

Three seemingly disparate stories in recent days help illustrate what climate scientists keep repeating — that empirical evidence indicating a warming world is widespread and robust, despite lingering and important uncertainties about how the world's climate system functions.

First up: news out of the World Meteorological Organization (WMO), a U.N.-sponsored organization, that atmospheric concentrations of greenhouse gases in the atmosphere have reached a record high when compared to data from prior to the industrial revolution in 1750.

 This is important because these greenhouse gases, most especially carbon dioxide (CO2), are helping to drive global temperatures higher and higher over the long-term.

Measurements of greenhouse gas concentrations in the atmosphere since 1958, taken at Mauna Loa Observatory in Hawaii. Ppm = number of molecules of the gas per million molecules of dry air. This graph is known as the iconic “Keeling Curve.” 

According to the newly released annual WMO “Greenhouse Gas Bulletin,” the average amount of three key warming gases — CO2, nitrous oxide, and methane — reached a new high in 2009 compared to preindustrial times. Carbon dioxide, for example, which is released when fossil fuels such as coal and oil are burned, has increased by about 38 percent since the preindustrial era, although the financial downturn put a temporary dent in the CO2 growth rate in 2009. The Bulletin states:

Carbon dioxide is the single most important anthropogenic greenhouse gas in the atmosphere… For about 10,000 years before the industrial revolution, the atmospheric abundance of CO2 was nearly constant at [about] 280 ppm. This level represented a balance among the atmosphere, the oceans and the biosphere. Since 1750, atmospheric CO2 has increased by 38 percent, primarily because of emissions from combustion of fossil fuels… deforestation and land-use change.

The consequences of these increasing greenhouse gases are already evident around the world, as scientists and others plying the ocean depths or scaling mountaintops can attest.

Now a new NASA-led study demonstrates that it's not just air, land, and sea temperatures that are warming — but also the temperatures of large inland lakes. According to the study, which was recently published in the journal Geophysical Research Letters, many lakes in the middle and northern latitudes have warmed rapidly in the past 25 years.

Such warming can have a ripple effect on lake ecology by making conditions intolerable for some species and more amenable to others, and contributing to harmful algae blooms that can create the lake-equivalents of ocean 'dead zones.'

For the study, scientists employed thermal infrared satellite imagery from National Oceanic and Atmospheric Administration (NOAA) and European Space Agency satellites to measure nighttime water temperatures during the summer in 167 large inland water bodies in the northern and southern hemispheres. The researchers focused on summer temperatures (July-September in the Northern Hemisphere and January-March in the Southern Hemisphere) because of challenges involved with obtaining sustained and reliable satellite temperature estimates during the winter, when many large lakes are ice-covered or hidden underneath clouds.

They reported an average warming rate of 0.81°F per decade, with some lake surfaces warming as much as 1.8°F per decade.

Although the warming trend was global, the study found the greatest temperature increases were in the mid-to-high latitudes of the Northern Hemisphere. Lakes in southern Siberia and Mongolia have warmed the most since 1985, but statistically significant warming trends were also evident in lakes in the U.S. Southwest, as well as in the Great Lakes. Such trends match up well with surface air temperature readings, as well as computer model projections of how the earth will respond to increasing concentrations of greenhouse gases in the atmosphere.

“The results suggest that climate strongly influences the surface temperature of inland water bodies worldwide,” the study states. The new research is particularly significant because it provides another independent dataset demonstrating warming temperatures around the world, apart from the surface temperature readings taken at thousands of sites around the world each day.

Interestingly, the study found that for some lakes, water temperatures have been increasing more rapidly than air temperatures have. The researchers cite evidence suggesting that one explanation for this may be that declining ice cover in wintertime is leading to a positive feedback, since ice-free waters absorb more solar radiation, and therefore warm more than ice-covered ones.

 Lastly, another analysis released last week - this time from the UK Met Office's Hadley Center - found “overwhelming evidence of warming in a wide range of climate indicators, not just surface temperature.” The report, timed for release with the U.N. climate change talks in Cancun, Mexico, distinguishes between temperature trends over many decades, and short-term trends. “Since the late 1970s the long-term rate of surface warming has been about 0.16°C per decade. However, over the last decade the rate of warming has decreased,” states a Met Office press release. “Natural variability within the climate system could explain all of this recent decrease. Other factors could have contributed,” including changes in stratospheric water vapor, solar output, and emissions of atmospheric particles known as aerosols that can affect the climate.

 The report concludes however that recent warming has actually been underestimated.

“The rate of warming has been underestimated in the last decade because of: changes to sea-surface temperature measurement practices; [and] strong warming in the Arctic—where there are fewer observations.”

The WMO data, inland lake study, and the Met Office's findings are just three examples of the steady drumbeat of scientific results pointing to a warming climate. Many studies of different aspects of this warming have detected the fingerprints of increased greenhouse gases from human activities.