"Six Degrees" is both the title of a new novel, and the upper limit (6.4 degrees actually) of temperature among the scenarios considered in a new Intergovernmental Panel on Climate Change (IPCC) report. Six degrees really would be Hell on Earth, in a cataclysm which extinguished most of all life. Warming seas would decompose methane-hydrates in sediments releasing methane fireballs to tear across the sky in spectacular almost cometary displays of portent - too late by then to warn us of anything; the damage would have been done! The planet would be swept by "hypercanes" too - giant hurricanes of unimaginable force and proportion, scouring the earth of its soil with flash-floods. Those few who might remain as witnesses to this lethal alternation of fire and rain would be living in caves in polar regions, since elsewhere the world would be too hot for survival.
The consensus is that a rise of 3 degrees by 2100 is more likely, but even that would mean that the rainforests would dry-out, ignite and burn uncontrolled turning their current deluging rain and oppressive humidity to desert. A huge allocation of carbon would be released too, thus adding to the atmospheric burden of CO2 and cooking the planet further still. It looks as though the coral reefs have had it anyway - even a rise of 2 degrees or so will render them almost extinct. Four degrees would melt the Arctic ice-caps, including its permafrost and so release yet more contributions to the greenhouse cocktail, in the form of methane, since methane hydrates are locked-into permafrosts as well as ocean sediments. The consequence of this would be wide-scale relocation of populations, from the drowned lands around the Nile Delta, Bangladesh and Shanghai, in numbers of perhaps 100 million. Even within Europe, deserts are appearing in southern Spain, Italy and Greece, and half of all species could be wiped-out if the planetary thermostat reached 4.4 degrees above present. Australia would become dependent on imported food since its own agriculture would literally dry-out.
There is no doubt in my mind that the world is warming - some parts of it are drying-up, while other regions see increased rain/snowfall. The Alpine regions are warmer and I have not seen so little glacial cover for twenty or so years in Switzerland. There is less precipitation too - a lethal combination for ski resorts. The average atmospheric concentration of water vapour is 4% higher than it was in 1970, in consequence of increased evaporation from warmer seas. Since water-vapour is a very potent greenhouse gas (far more so than either CO2 or methane) , a strong positive feedback can be expected on global temperatures. I have speculated previously that the growth of the East Antarctic ice sheet is due to increased condensation of water from the atmosphere into its cold regions. Meanwhile warmer ocean currents aid the melting of the Antarctic northern peninsular, which has been melting for several thousands of years, since after the last ice-age.
In a previous posting ("Carbon in the Sky") too, I worked out that at least since 1950, human emissions of CO2 seem to exceed the ability of the planet to soak them up by around 60%. The ratio of emission/absorption seems fairly constant; however, as the emissions increase, then so year-on-year does the rise in atmospheric CO2 levels. Hence while an increase of 1.4 parts per million per year on average might account for the rising atmospheric burden of CO2 until about 1995, since then the average annual rise is nearer 1.9 ppm. Indeed, we may be increasingly exceeding that 60% overload, and perhaps e.g. phytoplankton is dying-off, or the loss of forests, meaning that the CO2 levels are expected to get worse, and that essentially is the message from the ICPP report.
However, Peak Oil is with us, meaning that there will be an inevitable fall in our CO2 emissions because there will be less oil to burn as we run out of the light crude oil on which most of the modern globalised world is based. Since none of the putative new technologies, e.g. hydrogen or biofuels can anywhere near match the gargantuan quantities of fuel that we currently use for transportation it will see a massive decline, and we will increasingly live in localised conurbations. Hence, the real challenge facing humanity is not dealing with cutting CO2 emissions which will happen unavoidably whatever we do, but how to survive in the post-oil era that will arrive well before the year 2100.