Society is not on course to fulfil the Paris Agreement to limit global warming

Human activities have already caused the Earth’s surface to warm by more than 1°C since the industrial period of 1850–1900. Warming substantially greater than the global average is being experienced in most land regions: up to twice as large for hot extremes in mid-latitudes and more than three times larger in the cold season in the Arctic. The increased atmospheric warming has led to more frequent and intense heavy precipitation events at global scale, but also to an increase in the frequency and intensity of droughts in some regions. The additional warming has also led to Arctic sea ice retreat, permafrost thaw, and to melting of glaciers and ice sheets, which together with the thermal expansion of the oceans, have resulted in accelerating sea level rise. Non-climatic drivers such as land subsidence, partly human-caused, have also played an important role in increasing vulnerability to sea level rise.

Human-induced climate change has led to increases in the intensity and frequency of many extreme events, in particular hot extremes in all land regions, heavy precipitation in several regions and droughts in some regions. In many regions, changing patterns of precipitation and the melting of snow and ice are altering the volume and seasonal timing of water flows in rivers, affecting both the quantity and quality of water resources, and the potential occurrence of peak flow events. Climate zones are shifting, including expansion of arid zones and contraction of polar zones.

The heat-trapping effect of atmospheric greenhouse gases will persist for centuries to millennia, and the resultant continued increase in global temperature will have large adverse consequences. There is inertia in the climate system. While some changes in the natural system, such as ocean acidification, can be detected almost immediately and can be clearly attributed to anthropogenic influence, other effects, such as sea level rise, will gradually but inexorably reveal themselves over the next several centuries. They are equally   attributable to climate change, but the connection is less obvious to non-scientific observers because of the delay.

Ice loss from the Greenland and Antarctic ice sheets is already contributing to sea level rise. The unstable retreat of some Antarctic and Greenland glaciers may further accelerate sea level rise, possibly abruptly. Mass loss from the Greenland Ice Sheet could be irreversible in the foreseeable future. Risks of biodiversity loss and extinction increase greatly both for terrestrial and marine species as warming increases, with large increases for warming levels between 1.5 and 2°C and further increases in risk beyond 2°C warming.

Ocean warming, acidification and deoxygenation, permafrost degradation, and the extinction of species are phenomena that are highly relevant to human societies and ecosystem integrity but are effectively irreversible on century time scales. Other effects, such as marine heatwaves and the retreat of Arctic sea ice, may be reversible over a period of decades to centuries if the drivers of warming are reversed. Widespread disappearance of Arctic near-surface permafrost is projected to occur this century, 2 – 66% of the area is at risk under low emission scenarios, and 30 – 99% under high emission scenarios, releasing as much as 240 gigatonnes of carbon to the atmosphere, further accelerating climate change. Permafrost melting dries out the soil in some places, results in flooding in other places, and causes damage to infrastructure.

Rising concern about the climate has led to the Paris Agreement and other international accords to curb greenhouse gas emissions. The United Nations Framework Convention on Climate Change (UNFCCC), signed in 1992, led to the Kyoto Protocol in 1997, the first coordinated attempt to limit greenhouse gas emissions. The subsequent Paris Agreement of 2015 was the result of several years of intensive international efforts to reach an agreement between all countries on limiting climate change. It includes the aim of “holding the increase in the global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C above pre-industrial levels.”

In the light of different national circumstances, the Paris Agreement calls for “rapid reductions” of emissions to be achieved “on the basis of equity, and in the context of sustainable development and efforts to eradicate poverty.” The connections between eradicating poverty and reducing inequality and addressing climate change are embedded in the sustainable development goals.

Despite growing awareness and alarm about climate change, greenhouse gas emissions have continued to rise. Emissions of greenhouse gases increased from the equivalent of around 30 gigatonnes of carbon dioxide (GtCO2e) in 1970 to around 55 GtCO2e in 2019. In the absence of vigorous mitigation measures and policies, most projections show further increases in greenhouse gas emissions in the future, driven by increasing fossil fuel use, land-use changes and other human activities.

If society continues on its current emissions pathway, it will miss the target of keeping warming to well below 2°C, let alone that of stabilizing global warming at 1.5°C, and be on course for warming of more than 3°C. Taken together, the national climate mitigation pledges (known as Nationally Determined Contributions) made to date fall far short of the reductions needed to achieve the goals set under the Paris Agreement. Current pledges are more consistent with scenarios that lead to a warming well in excess of 3°C by the latter part of the century. Many countries are failing to achieve even the modest emissions reductions goals they set for themselves. Unless major emissions reductions are achieved by 2030, any chance of stabilizing global warming at 1.5°C will be lost. Typical scenarios aimed at holding warming well below 2°C or even to 1.5°C typically show a 25–50% reduction compared to 2010.

Scenarios in which warming temporarily exceeds the Paris Agreement goals around mid-century before falling rapidly depend heavily on the development of carbon dioxide removal technologies, whose ability to capture and store carbon dioxide at scale is as yet unproven and could lead to unintended negative impacts on biodiversity and food production.

Climate change amplifies existing risks and creates new risks for natural and human systems. Restricting global warming to 1.5°C with no or limited overshoot avoids many additional risks compared to a stabilization at 2°C, including reducing the risk of some irreversible impacts. At 2°C of warming and higher, the likelihood and magnitude of impacts rises steeply. For example, substantial further increases in hot temperature extremes in most inhabited land regions are projected at global warming of 2°C or more compared to warming of 1.5°C. There would also be further increases in heavy precipitation in several regions, and a higher probability of drought and precipitation deficits in some regions. Global mean sea level rise is projected to be around 10 centimetres less by the end of the twenty-first century in a 1.5°C warmer world compared to a 2°C warmer world. The probability of a sea ice-free Arctic Ocean during summer is substantially higher at 2°C compared to 1.5°C of global warming. The risks to ocean and terrestrial ecosystems, including the number of species at risk of accelerated extinction, increase more than proportionally to the change in global mean temperature; at 2°C, the number of species at risk is more than 30% higher than for 1.5°C, and higher temperature increases further magnify the threats.

Making Peace with Nature