Climate predictions and tipping points

United in science 2022: The world is heading in the wrong direction
Cities – responsible for up to 70% of human-caused emissions – will face increasing climate impacts (Image: cocoparisienne, Pixabay)
Cities – responsible for up to 70% of human-caused emissions – will face increasing climate impacts (Image: cocoparisienne, Pixabay)

Levels of atmospheric carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2 O) continue to rise. Preliminary analysis of the data from a subset of the Global Atmosphere Watch (GAW) Green House Gas (GHG) observational network demonstrated that CO2 concentrations exceeded 410 parts per million (ppm) during the whole of 2021. Additionally, concentrations during the seasonal peak of 2022 in the northern hemisphere reached 430 ppm at some background locations.

Climate science is clear: we are heading in the wrong direction, according to a new multi-agency report coordinated by the World Meteorological Organization (WMO), which highlights the huge gap between aspirations and reality. Without much more ambitious action, the physical and socioeconomic impacts of climate change will be increasingly devastating, it warns.

The report, United in Science, shows that greenhouse gas concentrations continue to rise to record highs. Fossil fuel emission rates are now above pre-pandemic levels after a temporary drop due to lockdowns. The ambition of emissions reduction pledges for 2030 needs to be seven times higher to be in line with the 1.5 °C goal of the Paris Agreement.

At a time when urgent action to address climate change is needed, the report provides unified scientific information to inform decision-makers and highlights some of the physical and socioeconomic impacts of the current and projected climate.

According to the WMO Global Atmosphere Watch, atmospheric greenhouse gas (GHG) concentrations continue to rise, despite emissions reductions in 2020 resulting from the COVID-19 pandemic lockdowns. The Global Carbon Project also notes that, in 2021, global fossil CO2 emissions returned to 2019 pre-pandemic levels after a large, but temporary, absolute drop in emissions due to widespread lockdowns. These conditions are leading to increasing global surface temperature and other climatic changes, as highlighted by the WMO State of the Global Climate 2021 report, which found the most recent seven years, 2015 to 2021, to be the warmest on record.

The UN Environment Programme’s latest Emissions Gap Report found that the full implementation of mitigation pledges made by countries (as of 4 November 2021) is insufficient and will not keep global warming below 1.5 °C above pre-industrial levels. The report also found that the ambition of these pledges would need to be four times higher to keep global temperature rise below 2 °C above pre-industrial levels and seven times higher to limit warming to 1.5 °C. Enhanced mitigation action is needed to prevent the goals of the Paris Agreement from slipping out of reach.

Without ambitious action, the physical and socioeconomic impacts of climate change will be devastating. Irreversible physical changes in the climate system, known as tipping points, cannot be ruled out and could have significant global and regional consequences. According to the Urban Climate Change Research Network, cities – responsible for up to 70% of human-caused emissions – will face increasing climate impacts that will intersect with socioeconomic inequalities. Additionally, the WMO World Weather Research Programme highlights that it is the world’s most vulnerable populations that will suffer the most, as has already been observed during recent extreme weather events.

Billions of people around the world are highly vulnerable to the impacts of climate change. As a result, adaptation and disaster risk reduction are crucial to lower the risks to climate impacts. According to WMO and the UN Office for Disaster Risk Reduction, early warning systems not only save lives and reduce losses and damages, but also contribute to disaster risk reduction, and support climate change adaptation. However, less than half of all countries in the world have these crucial systems and coverage is particularly low in vulnerable countries. To address this issue, the United Nations Secretary General António Guterres called for new action to ensure every person on Earth is protected by early warning systems in the next five years.

Additionally, the Intergovernmental Panel on Climate Change recently released highly anticipated Working Group reports covering The Physical Science Basis; Impacts, Adaptation and Vulnerability; and Mitigation of Climate Change, which are an integral part of its Sixth Assessment Report. These important reports identify the strength of scientific agreement in these different areas as well as where further research is needed.

The science is clear – urgent action is needed to mitigate emissions and adapt to our changing climate. The United Nations system, along with its partners, will continue to provide world-leading science to inform decision-making and support global climate action.

Key messages

Greenhouse Gas (GHG) Concentrations in the Atmosphere

Levels of atmospheric carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) continue to rise. The temporary reduction in CO2 emissions in 2020 during the pandemic had little impact on the growth of atmospheric concentrations (what remains in the atmosphere after CO2 is absorbed by the ocean and biosphere).

Data from all global locations, including flagship observatories at Mauna Loa (Hawaii, USA) and Cape Grim (Tasmania, Australia) indicate that levels of CO2 continued to increase in 2021 and 2022. In May 2022, CO2 concentration at Mauna Loa reached 420.99 ppm (419.13 ppm in 2021) and Cape Grim 413.37 ppm (411.25 ppm in May 2021).

Global Greenhouse Gas Emissions and Budgets

Global fossil CO2 emissions in 2021 returned to the pre-pandemic levels of 2019 after falling by 5.4% in 2020 due to widespread lockdowns. Preliminary data shows that global CO2 emissions in 2022 (January to May) are 1.2% above the levels recorded during the same period in 2019, driven by increases in the United States, India and most European countries.

Despite a strong fluctuation in global emissions over the past two and a half years, fossil CO2 emissions fell significantly in 23 countries (many European countries, Japan, Mexico and the USA) during the pre-pandemic decade of 2010–2019.

A quarter of GHG emissions from land-use change are associated with the trade of food between countries, of which more than three quarters are due to land clearing for agriculture, including grazing.

State of the Global Climate: 2018–2022

The most recent seven years, 2015 to 2021 were the warmest on record. The 2018–2022 global mean temperature average (based on data up to May or June 2022) is estimated to be 1.17 ± 0.13 °C above the 1850–1900 average. A La Niña event has had a slight cooling effect on temperatures in 2021/22 but this will be temporary.

Around 90% of the accumulated heat in the Earth system is stored in the ocean, the Ocean Heat Content for 2018–2022 was higher than in any other 5-year period, with ocean warming rates showing a particularly strong increase in the past two decades.

Global Climate Predictions for 2022–2026

The annual mean global near-surface temperature for each year from 2022-2026 is predicted to be between 1.1 °C and 1.7 °C higher than pre-industrial levels (1850-1900).

The likelihood of the annual mean global near-surface temperature temporarily exceeding 1.5 °C above pre-industrial levels for at least one of the next five years is 48% and is increasing with time. However, there is only a small probability (10%) that the five-year mean will exceed this threshold. The Paris Agreement level of 1.5 °C refers to long-term warming, but individual years above 1.5 °C are expected to occur with increasing regularity as global temperatures approach this long-term threshold.

There is a 93% probability that at least one year in the next five will be warmer than the warmest year on record, 2016, and that the mean temperature for 2022–2026 will be higher than that of the last five years

Tipping Points in the Climate System

Further research on tipping points will be crucial to help society better understand the costs, benefits and potential limitations of climate mitigation and adaptation in the future.

The Atlantic Meridional Overturning Circulation (AMOC) is an important driver of the distribution of heat, salt and water in the climate system, both regionally and globally. Recent research suggests AMOC may be weaker in the current climate than at any other time in the last millennium.

The melting of the polar ice sheets on Greenland and Antarctica is also considered a major tipping point and would have global consequences due to substantial additional sea-level rise for hundreds to thousands of years.

The combined effects of higher temperatures and humidity in some regions could reach dangerous levels in the next few decades, with physiological tipping points or thresholds beyond which outdoor human labor is no longer possible without technical assistance.

Climate Change and Cities

Cities – home to 55% of the global population, or 4.2 billion people – are responsible for up to 70% of human-caused emissions while also highly vulnerable to the impacts of climate change such as increased heavy precipitation, accelerated sea-level rise, acute and chronic coastal flooding and extreme heat, among other key risks. These impacts exacerbate socioeconomic challenges and inequalities.

Globally, by the 2050s, over 1.6 billion people living in over 970 cities will be regularly exposed to 3-month average temperatures reaching at least 35 °C (95 °F). Between March and May 2022, Delhi experienced five heat waves with record-breaking temperatures reaching up to 49.2 °C (120.5 °F). With half of Delhi’s population living in low-income settlements and highly vulnerable to extreme heat, this heatwave led to devastating socioeconomic and public health impacts.

Cities have an important role in addressing climate change by implementing inclusive, urgent and scaled-up mitigation action and increasing the adaptive capacity of billions of urban inhabitants. Now is the time to integrate adaptation and mitigation, coupled with sustainable development, into the ever-dynamic urban environment.

Early warning systems: Adapting to climate change and reducing disaster risk

Early warning systems are effective adaptation measure that save lives, reduce losses and damages, and are cost-effective. Less than half of countries in the world have reported the existence of Multi-Hazard Early Warning Systems (MHEWS), with coverage particularly low in Africa, Least Developed Countries and Small Island Developing States. A top international priority is to ensure that everyone on Earth is protected by MHEWS in the next five years. This will require collaboration across diverse actors and innovative financing solutions.

The full report can be accessed here

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