Nowhere to run anymore

May 27

Most of the problems people have with weather and climate come from extremes. When means shift a little, extremes can shift a lot. Today’s rare extremes become tomorrow regular disturbances, tomorrow extremes are unknown yet to us. How damaging these impacts will be to the economic and physical welfare of humankind depends on how much warming takes place and how well people adapt – both of which are currently unknowable.

Tropical cyclones (hurricanes in Atlantic and typhoons elsewhere) can only form over a sea or ocean with a surface temperature of 27C or more. The area where such temperatures are possible will definitely increase with warming. Their formation also requires that the wind be blowing at a similar speed close to the surface and at greater altitudes and this condition does not increase however more heat in the ocean means that those tropical cyclones which do get going become more intense. Hurricanes reaching category four or five become new normal. So, too does the rainfall associated with them, because warmer air holds more moisture. Extreme rainfall events of many sorts increase in warmer worlds.

The heat which powers hurricanes at sea can, on land kill directly. Humans cool themselves by sweating, a process that become less effective the more humid the atmosphere. Combining the heat and the humidity into levels of 35 C and above is lethal. Until recently it was thought that high level would not be seen until warming had continued for decades. A review of weather station data show that level was already being experienced for a brief period in South-East Asia, the Persian Gulf and the coastal south-west of American and that their frequency had doubled in the last fifty years. With 2.5 C of global warming above the pre-industrial level which is very probable in the second half of this century if action on emission is not significantly increased these lethal mixtures of heat and humidity will become a regular occurrence in parts of the humid subtropics.

Climates which people find liveable according to where historically they have lived change dramatically by rising temperatures. By 2070 many areas where people live today develop climates unlike any that people have lived before: south west of North America and north of South America, south of Europe, central Africa, south east Asia and coastal regions of Australia.

In the nearer term, there is an increased likelihood of heatwaves. Extreme heatwaves are becoming more frequent not only because temperatures are climbing. Warming inducing changes in the climate system can weaken the processes that normally move weather around the world allowing conditions to get stuck. Such stalling can be the difference between a hot week and a lethal month, or in winter a cold snap and a deep freeze.

Hot summers harm crops sensitive to temperatures above a certain threshold and through water stress. Milder winters allow pests to survive hurting yields. When unusually hot and dry conditions suck the moisture off the land, the subsequent droughts increase risk and severity of fires which increase the amount of lighting that causes more fires. Not only fire-prone Australia but also large swathes of northern Russia and Canadian forest or even Greenland woodlands may be lit in unusual infernos regularly. Dried out rivers, lakes and underground aquifers across the entire south-west of the USA as a result of the twenty years lasting megadrought will lead to frequent wildfires. Such droughts are linked to changing pattern of circulation in the ocean.

The longest term change that does not affect us yet fully is sea level. The sea’s rise comes from three different mechanisms- the expansion of the oceans as they absorb more heat, the addition of meltwater from shrinking glaciers on land and the physical break down of ice sheets such as those on Antarctica and Greenland. The first two factors are currently driving an increase about 1 cm every three years and will continue to do so. Such rises already erode coasts and increase flooding – especially when pushed inland by the surges intense storms produce. Storms become more destructive in their winds and their rains. Seawater submerging beaches and infiltrating aquifers.

If the stability of the great ice sheets is further disrupted by their slow collapse the sea levels rise many metres. It is widely believed there are no point of return after that. It is also possible they might break even if warming is kept to 1.5 C above the pre-industrial. There are other tipping points which could see ocean currents shift or deserts spread.

The impacts of climate change are already here…get yourself ready. Your anxiety does not help but your action does!