The problem: rising carbon dioxide in the atmosphere
The level of CO2, the main greenhouse gas, has been rising since the Industrial Revolution and is at its highest for about 4m years. The rate of the rise is even more striking, the fastest for 66m years, with scientists saying we are in “uncharted territory”.
The causes (I): fossil fuel burning
Billions of tonnes of CO2 are still pumped into the atmosphere every year from coal, oil and gas burning. The slight reduction in 2020 as a result of coronavirus lockdowns was no more than a “tiny blip” in the continuing buildup of greenhouse gases, according to the World Meteorological Organization, and emissions have rebounded.
The causes (II): forest destruction
The felling of forests for timber, cattle, soy and palm oil is a big contributor to CO2 emissions. It is also a significant cause of the annihilation of wildlife on Earth.
The causes (III): methane emissions
Methane is a powerful greenhouse gas and emissions are increasing faster than at any time in 40 years of observations. Farming, especially cattle, as well as fossil fuel extraction and landfill sites, are responsible. Warming wetlands may also be contributing.
The consequences: global temperature rise
The planet’s average temperature started to climb steadily two centuries ago, but has rocketed since the second world war as consumption and population have risen. Global heating means there is more energy in the atmosphere, making extreme weather events more frequent and more intense.
The consequences: rising sea levels
Sea levels are inexorably rising as ice on land melts and hotter oceans expand. Sea levels are slow to respond to global heating, so even if the temperature rise is restricted to 2C, one in five people in the world will eventually experience their cities being submerged, from New York, to London, to Shanghai.
The consequences: shrinking Arctic sea ice
As heating melts the sea ice, it reveals darker water that absorbs more of the sun’s heat, causing more heating – one example of the vicious circles in the climate system. Scientists think the changes in the Arctic may be responsible for worsened heatwaves and floods in Eurasia and North America.
The upside (I): wind and solar energy is soaring
Huge cost drops have helped renewable energy become the cheapest energy in many places and the rollout is projected to continue. The cost advantage over fossil fuels is even greater with the price rises following Russia’s invasion of Ukraine. But much government action is still required to reach the scale needed, and to tackle difficult sectors such as aviation and steel.
The upside (II): electric vehicles
The global fleet of electric cars and vans is still small compared with those running on fossil fuels. But sales are growing very fast and governments are setting end dates for the sale of petrol and diesel vehicles. Electric cars are cheaper to run, suggesting they will rapidly dominate.
The upside (III): battery costs
Renewable energy is intermittent, varying as the sun shines or wind blows. So storage is vital and the cost of batteries is plummeting. But other technologies with longer storage duration, such as green hydrogen, will also be needed.