Climate change: the defining issue of the twenty-first century
"Climate change is happening, humans are causing it, and I think this is perhaps the most serious environmental issue facing us." Bill Nye
Thanks to different climate proxies, especially ice cores, we can reconstruct climate over hundreds of thousands of years.
There is a strong and complex correlation between the concentrations of greenhouse gases in the atmosphere and the temperature on Earth: every greenhouse gas concentration variation matches a temperature swing.
Carbon Dioxide (CO2) and Methane (CH4) are the two main anthropogenic greenhouse gases. Their concentrations in the atmosphere are at their highest in 800,000 years.
"Climate risks escalate over time: some of the changes we are seeing were not expected to occur so soon - or at all." Dr. Michael Oppenheimer
Carbon dioxide is the main anthropogenic greenhouse gas. It is responsible for about 75% of the anthropogenic greenhouse effect.
Since the pre-industrial era, the carbon dioxide concentration in the atmosphere has risen by 50%, from 280 ppm to 421 ppm.
Most of this growth has occurred since 1970 and has come directly from fossil fuel combustion. Indeed, fossil fuels account for 80% of the global energy mix.
This sharp increase has had a critical impact on the average global temperature on Earth, which has grown by 1.2°C since the pre-industrial era.
"We need to reach carbon neutrality in 2050. Every half a degree matters." Valérie Masson-Delmotte
Since 2000, global fossil CO2 emissions have sharply increased, mainly because of China's emissions, which have almost tripled in 20 years.
China's CO2 emissions account for 31% of global CO2 emissions, the United States' ones 14% and Europe's ones 11%.
Those numbers must naturally be weighted by the size of the populations and by the historical responsibility of developed countries for climate change.
Coal use is a defining issue of climate warming. According to the IEA, about 44% of global CO2 emissions come from coal.China's coal consumption account for almost 50% of the global coal consumption.
It is worth to be noted that the Covid-19 crisis has had a significant impact on emissions.
+1°C, +2°C, +3°C, +4°C, +5°C, +6°C.......+7°C in 2100 ?
Since the pre-industrial era, the global average temperature on Earth has risen by 1.2°C. If the countries meet their Paris Agreement commitments (NDCs), climate warming should reach about 2.5°C in 2100, well above the 1.5°C target.
According to the UNEP "countries must collectively increase their NDC ambitions more than fivefold to get on track to the 1.5°C goal".
Furthermore, China's climate policy is very nebulous and India's energetic development remains in question.
Climate research institutes (including IPSL and CNRM) have elaborated new climate models: the CMIP6 models. According to the most recent ones, in the worst case global warming could reach 7°C at the end of the Twenty-First century.
Hundreds of millions of people have been affected by climate warming. Its intensity is unprecedented in history and its effects (heatwaves, droughts, floods, storms, sea level rise, etc.) will increase within the next decades. But to what extent ?
