Sunday, June 28, 2015

Lake Surfaces in the Temperature Record

Serious question: A paper in GRL last year found, using satellites, that lakes comprise about 3.7% of the nonglaciated land area on the planet.

They defined a "lake" as more than 2000 m2 in size -- about half a football field. They count 117 million of them, with a total size is 5 million km2 -- half the size of the U.S.

So the average lake size is 42,000 m2 (207 m)2.

Are the temperature trends of lake surfaces being monitored, as we do on land? If not, isn't that a potential bias in the long-term record? (I don't know which way it would go.) Or is it that the exclusion of lakes lead to a small enough error?

8 comments:

William Connolley said...

I don't actually know but I can speculate (of course): lake shores are attractive living places and so there will tend to be thermometer stations around the shores, and so (I'd guess) they're actually more densely monitored that the planetary average. And lakes, being water, are more uniform in temperature than the equivalent area of land.

WHT said...

In northern latitudes, lake "ice-out" dates are monitored and the results are striking.

David Appell said...

WHT: Yes, I've seen those, like for Lake Winnipesaukee (where I lived for several years):

https://en.wikipedia.org/wiki/Lake_Winnipesaukee_Ice-Out

Victor Venema said...

Yes, lake temperatures are monitored, but not as systematically as the air temperatures. There are no "weather services" responsible, which like for many ecological observations make maintaining long series hard.

The Global Lake Temperature Collaboration is collecting and analyzing lake temperatures. They show a strong trend. Between 1985 and 2009 the satellite lake temperatures in creased by 1.13°C or for comparison: 4.5°C per century.

This is stronger than the land temperatures, but at the moment it is not clear yet what is the reason for that. It could be ice albedo feedback for Northern lakes, changes in the observations (as always) and the land surface temperature trend might also be underestimated.

WHT, to lake (and river) ice freezing and break-up data there is this nice paper, showing impressing long-term changes:

Magnuson, John J., Dale M. Robertson, Barbara J. Benson, Randolf H. Wynne, David M. Livingstone, Tadashi Arai, Raymond A. Assel, Roger B. Barry, Virginia Card, Esko Kuusisto, Nick G. Granin, Terry D. Prowse, Kenton M. Stewart, Valery S. Vuglinski, 2000: Historical trends in lake and river ice cover in the Northern Hemisphere. Science, 289, pp. 1743-1746, doi: 10.1126/science.289.5485.1743.

Brian said...

I have nothing to contribute other than a related question: has the heat storage (and eventual release) capability of lakes been taken into account in monitoring the Earth's energy balance. I imagine the deep/large volume lakes might be more than rounding errors in these calculations, but maybe not.

Victor Venema said...

The above short comment has now been turned into a referenced blog post on the surprisingly fast changes in the temperature of lakes and the fast reductions in the freezing period of lakes and rivers.

We would expect lake temperatures to rise slower (more of the additional heat goes to evaporation than to warming), but it looks like they are warming faster than the air temperatures in the region.

Enjoy.

Lakes are warming at a surprisingly fast rate

Victor Venema said...

The above post has stimulated me to finally finish a post on the surprisingly fast changes in the temperature of lakes and the fast reductions in the freezing period of lakes and rivers.

We would expect lake temperatures to rise slower (more of the additional heat goes to evaporation than to warming), but it looks like they are warming faster than the air temperatures in the region.

Enjoy.

Lakes are warming at a surprisingly fast rate

David Appell said...

Thanks Victor. Sorry for the delay getting your comment published -- I've been away for awhile.