A 2009 study by Drew Shindell et al. shows that chemical interactions between emissions cause more global warming than previously estimated by the IPCC. The study shows that increases in global methane emissions have already caused a 26% decrease in hydroxyl (OH). Because of this, methane now persists longer in the atmosphere, before getting transformed into the less potent carbon dioxide.

A Centre for Atmospheric Science study suggests that sea ice loss may amplify permafrost warming, with an ice-free Arctic featuring a decrease in hydroxyl of up to 60% and an increase of tropospheric ozone (another greenhouse gas) of up to 60% over the Arctic.

Extension of methane’s lifetime further amplifies its greenhouse effect, especially for releases that are two or three times as large as current releases.

The graph on the right, based on data by Isaksen et al. (2011), shows how methane’s lifetime extends as more methane is released.

The image below, from a study by Dessus et al., shows how the impact of methane decreases over the years. In the first five years after its release, methane will have an impact more than 100 times as potent as a greenhouse gas compared to carbon dioxide.

The GWP for methane typically includes indirect effects of tropospheric ozone production and stratospheric water vapor production. The study by Isaksen et al. shows (image below) that a scenario of 7 times current methane levels (image below,medium light colors) would correspond with a radiative forcing of 3.6 W/m^-2.

Such an increase in methane would thus add more than double the entire current net anthropogenic warming (for comparison, see Wikipedia image below).

For many years, the amount of methane has remained stable at about 5 Gt annually (NOAA image below). A scenario of 7x this amount would lift the amount of methane in the atmosphere to about 35 Gt.

A scenario of seven times the amount of methane we’re used to having in the atmosphere would give the methane a lifetime of more than 18 years, so there’s no relief from this burden in sight, while this would triple the entire net effect of all emissions added by people since the industrial revolution.

What makes things even worse is that all this methane would initially be concentrated in the Arctic, whereas GWP for greenhouse gases is typically calculated under the assumption that the respective greenhouse gas is spread out globally.

All this methane will initially be concentrated locally, causing huge Arctic amplification of the greenhouse effect in summer, when the sun doesn’t set.

The methane will heat up the sea, causing further lack of of oxygen in the water, while algae start to bloom, making this worse, and lack of hydroxyl in the air.

In a vicious circle that will further accelerate the permafrost melt, this will cause further releases from permafrost and clathrates.

Back in 2009, I pointed at projections of a MIT study showing that, without rapid and dramatic action on global warming, global median surface temperature will rise by 9.4^oF (5.2^oC) by 2100.

The wheel on the right depicts the MIT’s estimate of the range of probability of potential global temperature rise by 2100 if no policy is enacted on curbing greenhouse gas emissions.

The wheel on the left assumes that aggressive policy is enacted, and projects a lower rise.

The projections show rises ranging up to 13.3^oF (7.4^oC), based on probabilities revealed by 400 simulations.

But even the worst-case scenario in the above MIT-study may actually understate the problem and the speed with which this may eventuate, since the model does not fully incorporate positive feedbacks such as large-scale melting of permafrost in arctic regions and subsequent release of large quantities of methane.

Several teams of scientists warn that we can expect a rise of 4^oC within decades. A rapid rise in temperature is likely to make the areas where most people now live uninhabitable, leaving humans, mammals and plants little on no time to migrate to cooler areas. The image below (edited from New Scientist) shows that the currently inhabited part of the planet would become largely uninhabitable with a global temperature rise of 4^oC.

Above image gives some suggestions as to action that can be taken, such as reforestation and construction of clean energy facilities. The image also shows that habitable areas may be restricted to the edges of the world where there’s little sunshine. A specific area can become uninhabitable due to sea level rises or heat stress. Humans simply cannot survive prolonged exposure to temperatures exceeding 95°F (35°C), explains Steven Sherwood. An area can also become uninhabitable due to recurring wildfires, floods, droughts, storms and further extreme weather events that cause erosion, desertification, crop losses and shortages of fresh water.

Back in 2007, I pointed at the danger of tipping points beyond which human beings face the risk of total extinction, particularly if many species of animals and plants that humans depend on will disappear. The boiling point analogy shows that there may be a window of time to act, like a silence before the storm. This realization should prompt us to speed up implementation of the necessary policies while we can. In fact, abrupt large releases of methane may close that window rather quickly, as described in Runaway Global Warming and The potential for methane releases in the Arctic to cause runaway global warming.

Posted by Sam Carana at 6/11/2011 05:48:00 PM Labels: arctic, clathrate, climate, climate change, greenhouse effect, methane, permafrost, tipping point