In brief: The world's lakes are warming
A global collaboration has revealed that climate change is affecting some of the world's lakes.
Recent studies have shown those lakes are warming significantly – faster than the surrounding air, in some cases – which has profound implications for the plants and animals living in them.
The Global Lake Temperature Collaboration, sponsored by the US National Science Foundation, NASA and the University of Nebraska, has been set up to better understand the dynamics of lake warming.
Thirty scientists from agencies worldwide are sharing data and expertise to develop an agreed standard for measuring lake water temperature trends at a global scale. New Zealand is represented by NIWA Freshwater Scientist Dr Piet Verburg.
The group met for the first time last June to analyse data from around 200 of the world's lakes, examining lake surface temperatures and vertical temperature profiles.
The world's lakes are warming "In New Zealand, the first good continuous lake temperature records only started in the 1990s, at Lake Brunner and at Lake Taupo," says Verburg.
"In exceptionally warm years, such as 1998, we see in the records from Lake Taupo that the bottom water warms more, because there has been less mixing with cool surface water during winter," he says.
Every winter, warm and cold water layers – hitherto separate – begin to mix. So to get an accurate picture of water temperature trends, researchers need records from the entire water column.
When he compared temperature records from Lake Tutira, in Hawke's Bay, from the early 1990s with readings from the last three years, he found that the lake had warmed by around one degree. "That's significant," he says, "because it's very important to lake processes like stratification and mixing, which affect the lake ecosystem through the distribution of oxygen and nutrients."
The threat of climate impacts makes global lake temperature data – from both in situ measurements and remote satellite sensing – increasingly valuable. Verburg says it's vital to monitor our lake temperatures as thoroughly as we record air temperatures. "We have 100 years of air temperature records from some places, which is why we we can say it has warmed by around one degree in the past century. Only if you have good monitoring data can you examine long-term trends.
"This is important to our understanding of what is going on in our lakes, and how climate change is affecting them."