16 de outubro de 2011

Evidências ...

Dois artigos. O primeiro é mais um ponto da situação. O segundo é uma tese sobre a origem da pequena idade do gelo: é convincente, e logo pode ser mais uma evidência .... Leituras recomendadas na totalidade.

What are the key findings of this scientific review?

We divide up the report according to changes to physical, hydrological, and ecological systems, as well as advances in technologies. As a whole, the literature paints a bleak picture. We are continuing to see accelerating change in many systems, with some changes happening much faster than initially envisioned.
Some of the key findings:
  • 2000-2009 was the warmest decade on record since 1880 (NASA).
  • The climate system has a number of different feedback mechanisms built into it, some of which are better known than others. New evidence suggests that as temperature rises, there may be positive feedbacks (processes that reinforce processes) through less cloud cover and in changes in aerosols, soils, peatlands, and Arctic ice cover, which can accelerate climate change impacts.
  • Observations show that multi-year winter sea ice area decreased by 42 percent between 2005 and 2008 and that there was a thinning of ∼0.6 m in multi-year ice thickness over the same 4 years (average thickness of the seasonal ice in midwinter is ∼2 m) (Kwok et al.).
  • Ocean acidification – caused by the buildup of carbon dioxide concentrations – was only recently recognized as a threat to coral in areas such as the Great Barrier Reef (and is happening much more quickly than anticipated (De’ath et al.)). It is now recognized as having implications for the entire ocean food web which is critical to whales, fish, and mollusks (snails and scallops) (Munday et al., Gooding et al. and Comeau et al.).
  • The rate of mass loss in the East Antarctic Ice Sheet may be greater than previously estimated (Chen et al.).
  • Based on physiological estimates, a global average temperature increase of 7° C, which is toward the extreme upper part of the range of current projections, would make large portions of the world uninhabitable to humans (Sherwood et al.).

Did Columbus Cause Europe's Little Ice Age? | Informed Comment

This story is irresistible for a world historian interested in climate change.Richard Nevle, a geochemist at Stanford, argues that the European advent in the New World, which killed 90% of the 80 million native Americans, caused the Little Ice Age.  The native peoples of the New World burned a lot of wood. When they largely didn’t exist anymore, because they suffered high mortality from a host of European diseases to which they had no immunity, they stopped putting carbon dioxide in the atmosphere. Instead, forests grew rapidly since they weren’t being chopped down anymore, and land wasn’t being cleared for agriculture. Forests take in carbon dioxide and exhale oxygen, plus they fix some carbon dioxide in the soil. They are what is called a “carbon sink,” though not a really efficient one, since much of the carbon they take out of the atmosphere eventually finds its way back there. I suspect the dramatic fall-off in the burning of fossil fuels was the much more important cause here.

Sem comentários: