ENVIRONMENT

Recent studies reveal significant warming of the world's lakes

Wednesday 3 October 2012, 2:23PM
By NIWA
210 views


Scientists from around the world that work on lakes are pooling data and expertise, to better understand global changes in lake temperature.

The collaboration, which comprises 30 key international scientists, is working to develop a unified approach to the measurement of lake water temperature trends at a global scale. New Zealand is represented by NIWA freshwater scientist Dr Piet Verburg.

The Global Lake Temperature Collaboration is sponsored by the National Science Foundation, NASA and University of Nebraska. At their first meeting, last June at the University of Nebraska-Lincoln, the working groups analysed data from roughly 200 lakes around the globe.

Recent studies have revealed significant warming of the world's lakes, and this rate of warming is, in many lakes, greater than that of the air temperature.

These rapid, unprecedented changes in lake temperature have profound implications for the plants and animals living in those lakes.

The potential impacts of the warming changes on lake ecosystems make it increasingly important for scientists with access to global lake temperature records to assemble and combine data. This includes both ‘in situ’ measurements made on individual lakes and temperature measurements from satellites which provide broader spatial coverage of the world’s lakes.

The data being analysed at the workshop includes not only lake surface temperatures, but also vertical temperature profiles for many of the lakes.

“In New Zealand, the first good continuous lake temperature records started only in the 1990s, at Lake Brunner and at Lake Taupo.

“In exceptionally warm years, such as 1998, we see in the records from Lake Taupo that the bottom water warms more, and that is because there has been less mixing with cool surface water during winter,” says Dr Verburg.

Every winter the whole of each of these lakes mixes, so the heat uptake from summer in the surface waters is mixed throughout the whole lake. To get an accurate record of increased water temperature, records from the whole of the water column are needed.

“In contrast to other international lake observations, the air temperature of the area around both lakes has increased over this period, but there is not yet substantial heating seen at the surface of either of these lakes,” says Dr Verburg.

“In New Zealand, we need good lake records,” says Dr Verburg. “We have excellent air temperature records, some of which date back 100 years, which is why we can say that air temperature has increased by around 1 degree in the past century. Only if you have good monitoring data can you examine long-term trends.”

This is important to understand what is going on in our lakes and how climate change is affecting our lakes.