Lake Temperature Data Over Decades Show Warming
Methane is increasing in the atmosphere, but many sources are poorly understood. Lakes at high northern latitudes are such a source. However, this may change with a new study published in Nature Geoscience. By compiling previously reported measurements made at a total of 733 northern water bodies — from small ponds formed by beavers to large lakes formed by permafrost thaw or ice-sheets — researchers are able to more accurately estimate emissions over large scales.
“The release of methane from northern lakes and ponds needs to be taken seriously. These waters are significant, contemporary sources because they cover large parts of the landscape. They are also likely to emit even more methane in the future,” says Martin Wik, PhD student at the Department of Geological Sciences and Bolin Centre for Climate Research, Stockholm University, who led the study.
With climate warming, particularly at high northern latitudes, longer ice-free seasons in combination with permafrost thaw is likely to fuel methane release from lakes, potentially causing their emissions to increase 20-50 precent before the end of this century. Such a change would likely generate a positive feedback on future warming, causing emissions to increase even further.
“This means that efforts to reduce human induced warming are even more urgent in order to minimize this type of feedback of natural greenhouse gas emissions. In a sense, every reduction in emissions from fossil fuels is a double victory,” says David Bastviken, Professor at Tema Environmental Change, Linköping University.
Source: January 4, 2016 – Stockholm University, ScienceDaily.com.
Climate change is rapidly warming lakes around the world, threatening freshwater supplies and ecosystems, according to a study spanning six continents.
The study is the largest of its kind and the first to use a combination of satellite temperature data and long-term ground measurements. A total of 235 lakes, representing more than half of the world’s freshwater supply, were monitored for at least 25 years. The research, published in Geophysical Research Letters, was announced today at the American Geophysical Union meeting.
The study, which was funded by NASA and the National Science Foundation, found lakes are warming an average of 0.61 degrees Fahrenheit (0.34 degrees Celsius) each decade. That’s greater than the warming rate of either the ocean or the atmosphere, and it can have profound effects, the scientists say.
Algal blooms, which can ultimately rob water of oxygen, are projected to increase 20 percent in lakes over the next century as warming rates increase. Algal blooms that are toxic to fish and animals would increase by 5 percent. If these rates continue, emissions of methane, a greenhouse gas 25 times more powerful than carbon dioxide on 100-year time scales, will increase 4 percent over the next decade.
“Society depends on surface water for the vast majority of human uses,” said co-author Stephanie Hampton, director of Washington State University’s Center for Environmental Research, Education and Outreach in Pullman. “Not just for drinking water, but manufacturing, for energy production, for irrigation of our crops. Protein from freshwater fish is especially important in the developing world.”
The temperature of water influences a host of its other properties critical to the health and viability of ecosystems. When temperature swings quickly and widely from the norm, life forms in a lake can change dramatically and even disappear.
“‘These results suggest that large changes in our lakes are not only unavoidable, but are probably already happening,” said lead author Catherine O’Reilly, associate professor of geology at Illinois State University, Normal. Earlier research by O’Reilly has seen declining productivity in lakes with rising temperatures.
Temperature increases close to or above the average .61 degrees F rise were seen in some of the world’s most popular waters, including Lake Tahoe (+.97 F by hand, +1.28 by satellite), the Dead Sea (+1.13 F), two reservoirs serving New York City, Seattle’s Lake Washington (+.49 F), and the Great Lakes Huron (+1.53 F by hand, +.79 by satellite), Michigan (+.76 F by hand, +.36 by satellite), Ontario (+.59 F) and Superior (+2.09 F by hand measurement, +1.44 F by satellite).
Study co-author Simon Hook, science division manager at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., said satellite measurements provide a broad view of lake temperatures over the entire globe. But they only measure surface temperature, while hand measurements can detect temperature changes throughout a lake. Also, while satellite measurements go back 30 years, some lake measurements go back more than a century.
“Combining the ground and satellite measurements provides the most comprehensive view of how lake temperatures are changing around the world,” he said.
The researchers said various climate factors are associated with the warming trend. In northern climates, lakes are losing their ice cover earlier, and many areas of the world have less cloud cover, exposing their waters more to the sun’s warming rays.
Previous work by Hook using satellite data indicated that many lake temperatures were warming faster than air temperature and that the greatest warming was observed at high latitudes, as seen in other climate warming studies. This new research confirmed those observations, with average warming rates of 1.3 degrees Fahrenheit (0.72 degrees Celsius) per decade at high latitudes.
Warm-water, tropical lakes may be seeing less dramatic temperature increases, but increased warming of these lakes can still have large negative impacts on fish. That can be particularly important in the African Great Lakes, where fish is an important source of food.
“We want to be careful that we don’t dismiss some of these lower rates of change,” said Hampton. “In warmer lakes, those temperature changes can be really important. They can be just as important as a higher rate of change in a cooler lake.”
In general, the researchers write, “The pervasive and rapid warming observed here signals the urgent need to incorporate climate impacts into vulnerability assessments and adaptation efforts for lakes.”
The Great Lakes are some of the world’s fastest warming lakes.
The decline of Great Lakes ice cover over the past several decades is contributing significantly to the rate of increase of summer water temperature, the study said.
The data also shows the world’s lakes are warming faster than the air around the lakes.
The study, published in the Geophysical Research Letters, finds that Lake Superior is warming the fastest of any of the Great Lakes.
The downside to warming waters is a more rapidly changing Great Lakes ecology. Warmer waters can negatively effect some native Great Lakes species, and increase invasive species.
Lake Superior is warming at a rate of 2.1°F per decade, according to the study.
Northern Lake Michigan is warming 0.4°F per decade, while southern Lake Michigan is warming at 0.76°F.
Northern Lake Huron is warming faster than southern Lake Huron. Northern Lake Huron is warming at a rate of 1.5°F and southern Lake Huron .79°F.
Lake Ontario is warming at .59°F per decade.
Lake Erie has been the slowest to warm at 0.15°F per decade.
The study looked at data from 1985 to 2009. It used satellite data, and actual water and air temperature measurements from buoys on the Great Lakes.
One would think the water would warm at the same rate as the air above it. The study showed this is not the case. Great Lakes water temperatures are actually rising about 50 percent faster than the overlying air temperatures.
An increasing number of ice-free days on each Great Lake are a major culprit in the warming, the study said. Lack of ice causes summer stratification of the water to occur earlier in the summer. Once summer stratification occurs, Great Lakes waters can warm faster on the surface.
Summer stratification means the water is warmer on the top surface of a lake, and then gets colder in gradually deeper water. This stratification develops during the spring and early summer. Coming out of winter, the surface water is coldest, and maybe ice covered, and the water gets warmer as you go to deeper depths. The temperature pattern then flip-flops heading into summer.
An older study found that this summer stratification is occurring nearly 14 days earlier in the last 27 years.
Although 2.1°F warming over a decade may not sound like a lot, that’s a 4.5°F water temperature rise on Lake Superior since 1979.
The study exemplifies the interdisciplinary work of WSU’s Grand Challenges, areas of research addressing some of society’s most complex issues. The study is also in keeping with the theme of the challenge “Sustainable Resources: Food, Energy, and Water,” which will develop strategies that link optimized agricultural practices, water management, and energy production.
150-year global ice record reveals major warming trend
September 7, 2000 By Brian Mattmiller
Sources as diverse as newspaper archives, transportation ledgers and religious observances, scientists have amassed lake and river ice records spanning the Northern Hemisphere that show a steady 150-year warming trend.
The study, which includes 39 records of either freeze dates or breakup dates from 1846 to 1995, represents one of the largest and longest records of observable climate data ever assembled. University limnologist John Magnuson led a team of 13 co-authors who contributed to the report, to be published in the Sept. 8 issue of the journal Science.
Sites ranges from Canada, Europe, Russia and Japan. Of those, 38 indicate a consistent warming pattern. The average rate of change over the 150-year period was 8.7 days later for freeze dates; and 9.8 days earlier for breakup dates. A smaller collection of records going well past 150 years also show a warming trend, at a slower rate.
“We think this is a very robust observation: It is clearly getting warmer in the Northern Hemisphere,” says Magnuson. “The importance of these records is that they come from very simple, direct human observations, making them very difficult to refute in any general way.”
Magnuson says the observational nature of the study is “both its strength and its weakness,” and the results do not offer specific proof that greenhouse gases are driving the warming trend. However, the findings are consistent with computer-generated models that have been developed to estimate climate change from greenhouse gases over a 125-year time period, he says.
The findings also correspond to an air temperature increase of 1.8 degrees Celsius over the past 150 years. A temperature change of 0.2 degrees Celsius typically translates to a one-day change in ice-on and ice-off dates.
Freeze dates were defined in the study as the observed period the lake or river was completely ice-covered; the breakup date was defined as the last ice breakup observed before the summer open-water phase.
Ice records have valuable attributes for climate researchers, Magnuson says. They can be gathered across a wide range of the globe, and in areas traditionally without weather stations. Their primary weakness is that early observers did not document the methods used.
“Of course, 10,000 years ago the Midwest was covered by ice, so we know it’s getting warmer,” he says. “What’s troubling and scary to people is that these rates in recent decades are so much faster.”
Climate models have predicted a doubling of total greenhouse gases in the next 30 years or so, a change that could potentially move the climate boundaries for fish and other organisms northward by about 300 miles, approximately the length of the state of Wisconsin, Magnuson says.
The records in this study are part of a decade-long project led by Magnuson and the UW–Madison Center for Limnology to build a database of lake and river ice records from around the world. The project was supported by the National Science Foundation’s Long-Term Ecological Research program, which emphasizes tracking and understanding global changes.
“It’s kind of a new science, you might call it network science,” Magnuson says. “We reached out to colleagues around the world and asked for these records. It turned out some people had very rich stores of data.”
The records in this study represent the longest and most intact of 746 records collected through the project. Some individual records are of astonishing lengths, with one dating back to the 9th century, another to the 15th century and two more to the early 1700s.
For example, Lake Suwa in Japan has a record dating back to 1443 that was kept by holy people of the Shinto religion. The religion had shrines on either side of the lake. Ice cover was recorded because of the belief that ice allowed deities on either side of the lake — one male, one female — to get together.
Lake Constance, a large lake on the border of Germany and Switzerland, has a peculiar record dating back to the 9th century. Two churches, one in either country, had a tradition of carrying a Madonna figure across the lake to the alternate church each year it froze.
Two other long records come from Canada’s Red and McKenzie rivers, which date back to the early 1700s and were kept because ice cover and open water were critical to the fur trade. Records from Grand Traverse Bay and Toronto Harbor, both on the shores of the Great Lakes, reflect their prominence as shipping ports.
Other records included in the study are from lakes Mendota, Monona and Geneva from Wisconsin; lakes Detroit and Minnetonka from Minnesota; lakes Oneida from New York and Moosehead from Maine; Lake Kallavesi from Finland; and the Angara River and Lake Baikal from eastern Russia.
Another finding in the study, based on the 184 ice records from 1950 to 1995, showed the variability in freeze and breakup dates increased in the last three decades. Magnuson says it might be related to intensification of global climate drivers such as the El Nino /La Nina effects in the Pacific Ocean.
Magnuson says the ecological effects of global warming are only beginning to be studied. But studies already exist that have shown the northern ranges of some butterflies and birds have been extending northward.