The Intergovernmental Panel on Climate Change (IPCC) – Sixth Assessment report

The Intergovernmental Panel on Climate Change (IPCC) – Sixth Assessment report

Climate change is widespread, rapid and intensifying, according to an influential UN report released in early August. This is the stark forecast in the Sixth Assessment Cycle report issued by the Intergovernmental Panel on Climate Change (IPCC).

The Intergovernmental Panel on Climate Change 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.

Each year IPCC scientists assess the thousands of scientific papers published 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. This synopsis forms the basis for the assessment reports.

The Sixth Assessment report was issued by Working Group I (IPPC has three working groups; Working Group I deals with the physical science basis of climate change; Working Group II deals with impacts, adaptation and vulnerability; and Working Group III deals with the mitigation of climate change), and states unequivocally that strong and sustained reductions in emissions of carbon dioxide are required urgently to limit the damage to the planet.

The Working Group I report is the first installment of the IPCC’s Sixth Assessment Report (AR6), which will be completed in 2022.

Unprecedented changes are being observed in every region and across the whole climate system as evidenced by the following:

  • CO₂ concentration is the highest 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
  • Sea levels are rising at the fastest rate in at least 3000 years
  • The area of arctic sea ice is at its lowest level in at least 1000 years
  • Glaciers are retreating at the fastest rate in at least 2000 years

The report provides new estimates of the probability of exceeding the global warming level of 1.5°C in the next decades and finds that unless there are immediate, rapid, and large-scale reductions in greenhouse gas emissions, limiting warming to close to 1.5°C or even 2°C will not be achievable.

The report shows that emissions of greenhouse gases from human (anthropogenic) activities today are responsible for approximately 1.1°C of global warming since 1850, and finds that averaged over the next 20 years, global temperature is expected to reach or exceed 1.5°C of warming resulting in increasing heat waves, longer warm seasons and shorter cold seasons.

In examining possible climate scenarios, the IPCC report lays out five possible scenarios to illustrate the climate response to various levels of greenhouse gas emissions. These scenarios are called Shared Socio-economic Pathways or SSPs and begin in 2015 and run to 2050.

The scenarios range from net negative CO₂ emissions, whereby more CO₂ is taken out of the atmosphere than emitted therein, to emissions staying at current levels, and progress to very high levels of greenhouse gas emissions. These pathways also take into account socio-economic assumptions, levels of climate change mitigation measures and air pollution controls.

Under all emissions scenarios considered (including the most benign one of net negative CO₂ emissions), the global surface temperature will continue to rise until at least the middle of this century. Global warming of 1.5°C would be exceeded this century under the 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 further states that even under the low emissions scenario, the 1.5°C warming level will likely be reached between now and 2040.

All five scenarios posit that global warming of 1.5°C and 2°C will be exceeded this century unless there are drastic reductions in CO₂ and other greenhouse gas emissions in the coming decades.

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. Several events we have witnessed in Ireland in recent years – such as the 2015-16 Storm Desmond and the 2018 drought and heatwave are almost certainly linked to global warming.

Unfortunately, the negative impact of past greenhouse gas emissions attributable to anthropogenic actions means that 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.

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, is also imperative. The latter is particularly important for Ireland, considering the significance of methane emissions in the agriculture sector.

In summary, the report makes it patently clear that achieving net-zero emissions is a requirement for stabilising CO₂ induced global surface temperature increase. One corollary of this is that from a risk perspective, undesired outcomes which hitherto had a low likelihood of occurrence, and a high severity of consequence can, no longer, be ruled out and become progressively more likely with additional warming. The precautionary principle applies now more than ever.