Recently, there have been some suggestions that “global warming” has been observed on Mars (e.g. here). These are based on observations of regional change around the South Polar Cap, but seem to have been extended into a “global” change, and used by some to infer an external common mechanism for global warming on Earth and Mars (e.g. here and here). But this is incorrect reasoning and based on faulty understanding of the data.
by Stefan Rahmstorf, Michael Mann, Rasmus Benestad, Gavin Schmidt, and William Connolley
On Monday August 29, Hurricane Katrina ravaged New Orleans, Louisiana and Missisippi, leaving a trail of destruction in her wake. It will be some time until the full toll of this hurricane can be assessed, but the devastating human and environmental impacts are already obvious.
Katrina was the most feared of all meteorological events, a major hurricane making landfall in a highly-populated low-lying region. In the wake of this devastation, many have questioned whether global warming may have contributed to this disaster. Could New Orleans be the first major U.S. city ravaged by human-caused climate change?
This question keeps coming back, although we know the answer very well: all of the recent CO2 increase in the atmosphere is due to human activities, in spite of the fact that both the oceans and the land biosphere respond to global warming. There is a lot of evidence to support this statement which has been explained in a previous posting here and in a letter in Physics Today . However, the most convincing arguments for scientists (based on isotopes and oxygen decreases in the atmosphere) may be hard to understand for the general public because they require a high level of scientific knowledge. I present simpler evidence of the same statement based on ocean observations, and I explain how we know that not only part of the atmospheric CO2 increase is due to human activities, but all of it.
Whenever three or more contrarians are gathered together, one will inevitably claim that water vapour is being unjustly neglected by ‘IPCC’ scientists. “Why isn’t water vapour acknowledged as a greenhouse gas?”, “Why does anyone even care about the other greenhouse gases since water vapour is 98% of the effect?”, “Why isn’t water vapour included in climate models?”, “Why isn’t included on the forcings bar charts?” etc. Any mainstream scientist present will trot out the standard response that water vapour is indeed an important greenhouse gas, it is included in all climate models, but it is a feedback and not a forcing. From personal experience, I am aware that these distinctions are not clear to many, and so here is a more in-depth response (see also this other attempt).