Climate change is widespread, rapid and intensifying, according to an influential UN report released last week.
The Intergovernmental Panel on Climate Change has said strong and sustained reductions in emissions of carbon dioxide are required urgently to limit the damage to the planet.
The first instalment of the IPCC's sixth assessment report was approved by 195 member governments on Friday, 6th August. It is unequivocal in its finding that human activity is responsible for climate change.
Scientists are observing unprecedented changes in every region and across the whole climate system. The planet is warmer, Arctic ice is shrinking, and sea levels are rising.
The report finds that human-induced climate change is the main driver of heatwaves and is likely the main driver for extreme rain. It said unless there were immediate, rapid and large-scale reductions in greenhouse gas emissions, limiting global warming to close to 1.5°C or even 2°C will be beyond reach.
The report contains the starkest warnings yet about the state of the planet and the damage caused by human activity. Where once scientists were less than certain about some causes of climate change, the hundreds of experts who contributed to this report have said it is "unequivocal that human influence has warmed the atmosphere, ocean and land".
Increases in greenhouse gases are unequivocally caused by human activity and have been increasing since 2011, when the last measurements were taken for the fifth assessment report.
Each of the last four decades has been warmer than any decade that preceded it since 1850, with the earth now 1.1C hotter than pre-industrial times.
The IPCC uses years 1850-1900 as an approximation for pre-industrial conditions due to the available data to estimate global surface temperature.
It is worth noting that in the Paris Climate Agreement, commitments were made to limit global warming to well below 2C, preferably to 1.5C compared to pre-industrial levels.
Human influence is very likely the main driver of the global retreat of glaciers and decrease in Arctic sea ice, while it is extremely likely that humans are responsible for the warming of the upper ocean.
The report also says it is virtually certain that human-caused CO₂ emissions are the main driver of acidification of the open ocean. Furthermore, human influence is very likely the main driver of increases in mean sea levels.
There is more CO₂ in the atmosphere than any time in at least 2 million years. Methane and nitrous oxide, which are also greenhouse gases, are at higher concentrations than at any time in at least 800,000 years.
Since the last report was published in 2013, scientists are more certain that human-induced climate change is affecting weather and climate extremes in every region across the globe. It is virtually certain that hot extremes, including heatwaves, have become more frequent and more intense across most land regions since the 1950s.
"Some recent hot extremes observed over the past decade would have been extremely unlikely to occur without human influence on the climate system," it states.
Heavy precipitation events, such as rain and snow, have increased since the 1950s also, for which human induced climate change is the likely cause.
The authors of the report will take no comfort in the fact that it is being published in a season that has seen hundreds of wildfires across Europe, Siberia and parts of the US, unprecedented flooding in China, and record high temperatures in North America, but it is illustrative of the damage caused by climate change.
In examining possible climate futures, the IPCC report lays out five possible scenarios to illustrate the climate response to various levels of greenhouse gas emissions, land use and air pollution.
They are called Shared Socio-economic Pathways or SSPs and they start in 2015 - lasting until 2050.
They range from net negative CO₂ emissions, whereby more CO₂ is taken out than emitted, include emissions staying at current levels, and progress to very high greenhouse gas emissions.
These models also take in socio-economic assumptions, levels of climate change mitigation measures and air pollution controls.
While it will not come as a surprise to those working in the field, it is quite stark to be reminded that the global surface temperature will continue to rise until at least the mid-century under all emissions scenarios considered.
Furthermore, global warming of 1.5C and 2C will be exceeded this century unless there are drastic reductions in CO₂ and other greenhouse gas emissions in the coming decades.
The report states global warming of 1.5C relative to pre-industrial times would be exceeded this century under intermediate, high and very high scenarios considered in the report. For context, the intermediate scenario assumes CO₂ emissions remain at current levels until 2050.
The report says that even under the low emissions scenario, the 1.5C warming level is more likely than not to be reached in the near term - i.e. between now and 2040.
If a grain of good news is to be found within these projections, it is that under the very low greenhouse gas emissions scenario, it is more likely than not that the global surface temperature would decline back to below 1.5C towards the end of the 21st century.
The report also cautions that many changes in the climate system become larger in direct relation to increasing global warming including the frequency and intensity of heatwaves, heavy precipitation, droughts in some regions, proportion of tropical cyclones, as well as reductions in Arctic ice.
With every additional increment of global warming, changes in extremes continue to become larger. Some of the changes already brought about by human activity are irreversible for centuries to millennia, especially changes in the ocean temperature, ice sheets and global sea level.
So, past greenhouse gas emissions have already done their worst in these areas, certainly for any human alive today, and their grandchildren.
The oceans will continue to warm up for hundreds to thousands of years. Glaciers will continue to melt for decades or centuries and the mean sea level will continue to rise for the rest of the 21st century.
The report is intended as a reality check, according to IPCC Working Group 1 Co-chair Valérie Masson-Delmotte, who adds that "it's been clear for decades that the Earth's climate is changing and the role of human influence on the climate system is undisputed".
If any solace is to be taken from the report, it is that human actions still have the potential to determine the future course of climate.
"Stabilising the climate will require strong, rapid, and sustained reductions in greenhouse gas emissions, and reaching net zero CO₂ emissions. Limiting other greenhouse gases and air pollutants, especially methane, could have benefits both for health and the climate," said co-chair Panmao Zhai.
The renewed focus on methane is one for Ireland to take note of, considering the significant agriculture sector.
In the section on Limiting Future Climate Change, the report says that limiting global warming to a specific level will require reaching at least net zero CO₂ emissions, along with strong reductions in other greenhouse gas emissions. Strong, rapid and sustained reductions in methane emissions are also desirable.
Every tonne of CO₂ adds to global warming, and it is linear, meaning that more emissions equal higher temperatures. This means that reaching net zero CO₂ emissions is required to stabilise global warming at any level, but if the aim is to keep within a target temperature (remember the commitment within the Paris Agreement to keep temperatures below 2C or preferably below 1.5C), then emissions must be kept within a carbon budget.
Another nugget of good news in this section is that under the low and very low greenhouse gas scenarios, there would be rapid and sustained effects to limit human-caused climate change, compared to scenarios with high or very high emissions.
The report makes it patently clear that achieving net zero emissions is a requirement for stabilising CO₂ induced global surface temperature increase.
About the IPCC
The Intergovernmental Panel on Climate Change (IPCC) is the UN body for assessing the science related to climate change. It was established by the United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO) in 1988 to provide political leaders with periodic scientific assessments concerning climate change.
Thousands of people from all over the world contribute to the work of the IPCC. For the assessment reports, IPCC scientists volunteer their time to assess the thousands of scientific papers published each year to provide a comprehensive summary of what is known about the drivers of climate change, its impacts and future risks, and how adaptation and mitigation can reduce those risks.
The IPCC has three working groups: Working Group I, dealing with the physical science basis of climate change; Working Group II, dealing with impacts, adaptation and vulnerability; and Working Group III, dealing with the mitigation of climate change. It also has a Task Force on National Greenhouse Gas Inventories that develops methodologies for estimating emissions and removals of greenhouse gases.
About the Sixth Assessment Cycle
Comprehensive scientific assessment reports are published every 6 to 7 years; the latest, the Fifth Assessment Report, was completed in 2014 and provided the main scientific input to the Paris Agreement.
The IPCC also publishes special reports on more specific issues between assessment reports.
Global Warming of 1.5°C, an IPCC special report on the impacts of global warming of 1.5 degrees Celsius above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty was launched in October 2018.
Climate Change and Land, an IPCC special report on climate change, desertification, land degradation, sustainable land management, food security, and greenhouse gas fluxes in terrestrial ecosystems was launched in August 2019.
The Special Report on the Ocean and Cryosphere in a Changing Climate was released in September 2019.
In May 2019 the IPCC released the 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories an update to the methodology used by governments to estimate their greenhouse gas emissions and removals.
The contributions of the three IPCC Working Groups to the Sixth Assessment Report are currently under preparation.
The concluding Synthesis Report is due in 2022.