The Fourth Assessment Report of the Intergovernmental Panel on Climate change (IPCC) predicts that the global temperature could rise by a possible 1.1°C to 6.4°C this century, Its best estimate is 4°C. While this does not seem much on a daily basis, globally, even 1°C can affect millions of people. The effect of a 6°C rise could lead to humanity's extinction.
At the end of the Permian period, 251 million years ago, an estimated 95 per cent of marine species and 70 per cent of land species were killed off when temperatures were estimated to be about 6°C higher than today.
Life on Earth did survive the 6°C increase but this increase took place over a 10,000-year period. Human releases of carbon dioxide are occurring at a greater rate than at any time in the history of life on Earth.
No one knows for sure if the Earth will heat up by 6°C but it is possible, also if it did heat up it is uncertain what would happen to life on earth. Here is one possible senario set out by the writer Mark Lynas who studied the historical records to examine the potential effects of temperature rises up to six degrees. Here is a summary of his findings.
The Gulf Stream could switch off leading to icy winters in Europe. Deserts spread across parts of the United States. The Arctic ice begins to melt. Coral reefs are wiped out around the world. Many mountain glaciers will be lost. As permafrost melts, landslides occur throughout the Alps.
European summers will be plagued by heat waves as strong as the killer of 2003. Greenland tips towards irreversible melt. Rising sea levels would devastate vulnerable coastal areas and cities including New York, London, Shanghai and Kolkata. Many species of plankton will be wiped out. The Polar Bear and Walrus become extinct.
Drought and wild fires rage across the Amazon leading to the decline of the rainforest. Deserts spread across Africa. Water shortages threaten Australia, India, Pakistan and Peru. Hurricanes increase in intensity. In northern Europe and the United Kingdom, summer drought will alternate with extreme winter flooding as torrential rainstorms sweep in from the Atlantic.
The whole Arctic Ocean ice cap will disappear. The West Antarctic ice sheet collapses, pumping 5 metres of water into global sea levels. In Europe, new deserts will be spreading in Italy, Spain, Greece and Turkey. The Alps will be so denuded of snow and ice that they resemble the rocky moonscapes of today's High Atlas.
Desert Belts spread across Europe, Asia and America. The Earth is hotter than at any time in the last 55 million years. It is likely that there is no ice at either pole. Most of the world is uninhabitable. As sea temperatures rise, methane hydrates are released from the seabed sparking a surge in global temperatures. The possible collapse of the seabed could give rise to massive tsunamis.
Huge firestorms sweep the planet as methane hydrate fireballs ignite. Seas release poisonous hydrogen sulphide. Deserts invade central Europe and may even reach close to the Arctic Circle. Most of life on Earth has been extinguished. Humanity's survival is in question