Extreme weather conditions – floods, droughts, wild fires, heat waves, hurricanes, blizzards -are now more frequent and more severe.
The energy that creates weather comes from the sun. The sun’s heat warms land, sea and air where differences in temperature create ocean currents and air currents – winds. When air moves across the seas it picks up moisture which ultimately becomes rain. The hotter the air the more water is taken up and held in the air. Again heat becomes a determinate of rain fall patterns – both quantity and intensity of rain fall (or snow etc) – eg monsoons in India after their hot season.
Air, land and sea are all heated directly by the sun. They are also heated indirectly by radiant heat from the earth. During the course of a day, in the absence of cloud cover, air temperatures will rise further as the heat from the sun is supplemented by heat radiating back from the earth. If the lack of cloud cover persists overnight, the radiant heat is lost into the upper atmospheres and the air temperatures drop. If however it is a cloudy night, the cloud will act like insulation keeping in the warmer temperatures.
Given that the sun has always been there, why are temperatures now increasing at a rate that are creating extreme weather events?
The Earth’s atmosphere is a mix of oxygen, nitrogen, carbon dioxide plus smaller quantities of other gases. Of these carbon dioxide is particularly good at absorbing heat and thus preventing extremely low temperatures when the earth’s surface is not receiving direct sunlight. Since the beginning of the Industrial Age we humans have been burning increasingly large amounts of fossil fuels such as coal, oil and gas. As these burn they release carbon dioxide. As levels of carbon dioxide in the atmosphere have increased so the insulating effect has also increased, and with it global temperatures – and with that an increase in extreme weather events.
|Global annual average temperature (as measured over both land and oceans) has increased by more than 1.5°F since 1880 (through 2012). Red bars show temperatures above the long-term average, and blue bars indicate temperatures below the long-term average. The black line shows atmospheric carbon dioxide (CO2) concentration in parts per million (ppm), indicating a clear long-term global warming trend.|
(Figure source: 2014 National Climate Assessment, updated from Karl et al. 2009)
The UN reported that across the world, between 2000-2019, there were 7,348 major disasters, claiming 1.23 million lives, affecting 4.2 billion people and causing £2.3tn in economic losses. Whilst in the UK flooding affected the Midlands and northern England in 2019 after the wettest November on record, and again in 2020 affecting Wales and southern England. The freezing temperatures of the ‘Beast from the East’ in February 2018 were followed by a heat wave from May to July with wild fires in areas near Manchester.
Since 1950 carbon levels in the atmosphere have risen from 311 parts per million to the current level of 414 ppm whilst average global temperatures have risen by just under 1C. The Paris Agreement set out to keep global temperature rises below 2C max and ideally below 1.5C, requiring global carbon dioxide emissions must be reduced to net zero by 2050. As this is not going to reduce temperatures below where they are now, extreme weather events are something we have to accept and adapt to.
Adapting to our new climate is one issue that will be addressed at the COP26 climate conference. It is also something that we can work at too. Insulating homes not only keeps them warmer in colder months, it also keeps them cooler in hot months. Win win plus reduces energy needs for cooling / heating. Planting trees creates shade and because of the way they ‘breathe’ reduce temperatures further by absorbing heat. In Rotterdam a 10% increase in tree cover produced a 1.3C reduction in temperatures ( Klok et al. 2012). Trees also lock away carbon dioxide and slow the rate at which rain water fills soils and drains so reducing the risk of flooding. A further win win solution.
Urban areas heat up faster than others because they have large areas of concrete and tarmac which readily radiate the sun’s heat back into the atmosphere. Reducing these or replacing them with grass or vegetative cover again reduces high summer temperatures. Creating cool areas around buildings with verandas, planting in trellises and planting in general will cool the air coming into the buildings as well as providing areas of shelter from the heat.