Since the industrial revolution, human activities and societies have been structured by the use of fossil fuels, with a strong impact on the climate. Preserving an inhabitable planet in the 21st century now represents an immense challenge.
A historical concentration
The concentrations of greenhouse gases in the atmosphere are already higher than ever during the history of homo sapiens (see Vital Signs of the Planet for the live concentration of carbon dioxyde and historical charts covering the previous 800,000 years). These concentrations continue to increase each year in response to significant annual anthropogenic emissions (see Global Carbon Atlas for a map of yearly emissions per country).
An already significant temperature rise
These concentrations have already caused an increase of 1°C of the average global temperature with respect to pre-industrial levels (see NASA's Vital Signs of the Planet for a graph of the temperature anomaly over time). Even heroic changes in our societies will not avoid an increase of at least 1.5°C by the end of the 21st century, which will already have huge impacts on Nature and humans (see Chapter 3 of IPCC's 2018 report on the impacts of a 1.5°C rise).
A very limited carbon budget
According to IPCC's 2018 report, the remaining carbon budget starting January 1st, 2020, is of 240 GtCO2 in order to have a 66% chance of limiting the temperature rise to 1,5°C, or of 990 GtCO2 in order to have a 66% chance of limiting the temperature rise to 2°C (see Table 2.2 of Chapter 2).
Humanity has already consumed most of its total carbon budget (see Mercator Research Institute's Carbon Clock for the corresponding remaining time based on current annual emissions, or Open Climate Data's Climate Spirals for nice visual representations).
The planned fossil fuels productions up to 2030 already exceed the 1,5°C budget (see the Production Gap report). For more on the notion of carbon budget, see Global Carbon Project's Carbon Budget Report.
An insufficient worldwide agreement
In December 2015, 196 state parties adopted the Paris agreement, whose stated goal is to maintain the temperature rise well below 2°C and try to limit it to 1.5°C. Unlike the previous agreement, the Kyoto Protocol, the Paris agreement neither sets emission reduction targets or emissions caps for each country, nor defines enforcement mechanisms. Instead, each country has been invited to define its own nationally determined contribution and re-evaluate it periodically.
Currently, not only is the sum of the pledges made by countries incompatible with limiting the temperature rise to 2°C, but the enforced and planned policies in each country are insufficient to meet the national targets (see Climate Action Tracker for a per-country analysis).