The Forum > Article Comments > Copenhagen: things fall apart and an uncertain future looms > Comments
Copenhagen: things fall apart and an uncertain future looms : Comments
By Bill McKibben, published 24/12/2009The Copenhagen summit turned out to be little more than a charade.
- Pages:
-
- 1
- 2
- 3
- ...
- 7
- 8
- 9
- Page 10
-
- All
"The IPCC notes that between 1750 and 2005, the radiative forcing from the sun increased by 0.12 watt/square-meter—less than a tenth of the net forcings from human activities (1.6 W/m2). The largest uncertainty in that comparison comes from the estimated effects of aerosols in the atmosphere, which can variously shade Earth or warm it. Even granting the maximum uncertainties to these estimates, however, the increase in human influence on climate exceeds that of any solar variation." "The most recent contrarian fad is based largely on work by Henrik Svensmark of the Technical University of Denmark, who argues that the sun's influence on cosmic rays needs to be considered. Cosmic rays entering the atmosphere help to seed the formation of aerosols and clouds that reflect sunlight. In Svensmark's theory, the high solar magnetic activity over the past 50 years has shielded Earth from cosmic rays and allowed exceptional heating; but now that the sun is more magnetically quiet again, global warming will reverse. Svensmark claims that, in his model, temperature changes correlate better with cosmic ray levels and solar magnetic activity than with other greenhouse factors. Svensmark's theory has so far not persuaded most climatologists, however, because of weaknesses in its evidence. In particular, there do not seem to be clear long-term trends in the cosmic ray influxes or in the clouds that they are suppose to form, and his model does not explain (as greenhouse explanations do) some of the observed patterns in how the world is getting warmer (such as that more of the warming occurs at night). For now, at least, cosmic rays remain a less plausible culprit in climate change.' "And the apparent warming seen on Mars? It is based on a very small base of measurements, so it may not represent a true trend. Too little is yet known about what governs the Martian climate to be sure, but a period of heavy dust storms on the planet that made its surface relatively dark might have increased the amount of absorbed sunlight and raised temperatures."