What the new IPCC report on climate change says

9 August 20213 years ago babelfish

All the most important indicators of the components of the climate system (atmosphere, oceans, ice) are changing at a speed never seen in the last centuries and millennia. The analysis by Annalisa Cherchi, Susanna Corti and Sandro Fuzzi, Lead Authors Ipcc Wg I Institute of Atmospheric and Climate Sciences National Research Council (Cnr) Bologna

Compared to the previous IPCC Report (AR5, 2013), new and more detailed observations, combined with increasingly improved climate models, have made it possible to deepen the knowledge and quantification of the anthropogenic effect on the Earth's climate, in any case already ascertained for at least a decade. .

The anthropogenic emissions of the main greenhouse gases have further increased, reaching concentrations of 410 parts per million (ppm) for CO 2 and 1,866 parts per billion (ppb) for methane in 2019.
The global average temperature of the planet in the decade 2011-2020 was 1.09 ° C higher than that of the period 1850-1900, with a more accentuated warming on land masses than in the ocean.
Most of the observed global warming is caused by greenhouse gas emissions from human activities.
As a result of global warming, the average level of sea level rise between 1901 and 2020 was 20 cm, with an average growth of 1.35 mm / year from 1901 to 1990 and accelerated growth of 3.7 mm / year. between 2006 and 2018.

All the most important indicators of the components of the climate system (atmosphere, oceans, ice) stand
changing at a speed never seen in the last centuries and millennia

The concentration of the main greenhouse gases is today the highest in the last 800,000 years.
Over the past 50 years, the Earth's temperature has grown at a rate that is unmatched in the past 2000 years.
In the last decade, the Arctic ice extent during the summer has been the lowest in the last 1000 years, and the reduction in the extent of terrestrial glaciers is unprecedented in the last 2000 years.
Mean sea level rise has been growing at a rate never experienced before, at least in the past 3,000 years, and ocean water acidification is proceeding at a rate never seen before, at least in the past 26,000 years.

COVID-19, AIR QUALITY AND CLIMATE

A completely unpredictable and unexpected phenomenon, the pandemic due to the COVID-19 virus, has made it possible to conduct an otherwise unthinkable experiment: the very short time reduction in emissions of atmospheric pollutants and greenhouse gases due to lockdowns practically all over the world. While the reduction in pollutant emissions has led to an albeit temporary improvement in air quality globally, the 7% reduction in global CO 2 emissions, a huge reduction never experienced in past decades, has had no effect on concentration. of CO 2 in the atmosphere and, consequently, no appreciable effect on the planet's temperature.

This is because, while the reduction of the emissions of the main pollutants, which remain in the atmosphere for a few days or, at most, for a few months, has a rapid effect on their concentration with a considerable benefit on human health and the environment in general, at the on the contrary, in order to combat global warming, reductions in the concentration of CO 2, which remains in the atmosphere for hundreds of years, and of other greenhouse gases that are sustained over time and of large amounts are necessary until complete decarbonisation.

OUR POSSIBLE FUTURE

In this Report, possible future climates are simulated on the basis of five possible future scenarios (Shared Socioeconomic Pathways, SSPs) which describe contexts in which there is no substantial mitigation with respect to CO 2 emissions (the SSP7.0 and SSP8 scenarios .5), an intermediate context, where mitigation is modest (SSP4.5) and contexts describing low CO 2 scenarios with zero emissions reached in the second half of the 21st century (SSP2.6 and SSP1.9).

On this basis:

The global surface temperature of the Earth will continue to increase at least until the middle of the current century in all the emission scenarios considered. Global warming levels of 1.5 ° C and 2 ° C above pre-industrial levels will be surpassed by the end of the 21st century unless there are profound reductions in CO 2 and carbon emissions over the next few decades. other greenhouse gases.
In the scenario with the lowest estimated CO 2 emissions (SSP1.9), corresponding to a decrease in global greenhouse gas emissions from 2020 onwards and the achievement of net CO 2 emissions of zero in the 2050s, global warming during the 21st century it is extremely likely that it will remain below 2 ° C.
Many of the changes already observed in the climate system, including increased frequency and intensity of temperature extremes, heat waves, heavy rainfall, drought, Arctic sea ice loss, snowpack and permafrost, will become more intense as warming increases. global.
Further global warming is expected to intensify the global water cycle, including its variability and the severity of wet and dry events.
It can be argued that every half degree of global warming causes a clearly perceptible increase in the frequency and duration of temperature extremes (heat waves), the intensity of heavy rainfall and drought in some regions of the planet.
Further warming of the climate is expected to further amplify thawing of permafrost and the loss of seasonal snow cover, land ice and Arctic sea ice. The Arctic is likely to be virtually free of sea ice in September (the month when it reaches its annual low) at least once before 2050 in all emission scenarios, with more frequent events for higher warming levels.
In scenarios with high CO 2 emissions, the carbon sink capacity of the oceans and terrestrial ecosystems is expected to become less effective in slowing the growth rate of atmospheric CO 2.
There are consequences of ongoing climate change that are irreversible over time scales of the order of hundreds of years. Notably this is true of changes affecting the ocean, Arctic sea ice and sea level (which will continue to rise throughout the 21st century).

The reduction of CO2 emissions will bring positive effects on air quality, observable on a time scale of a few years. Otherwise, the effects on the planet's temperature will only be visible after many decades. Hence the extreme urgency of timely and substantial interventions to reduce climate-altering emissions.

CLIMATIC INFORMATION ON A REGIONAL SCALE

Compared to the previous AR5 Report, scientific and technological progress, as well as greater awareness of the type of information requested by users, has led to an improvement in the quantity and quality of climate information, especially at a regional scale. This sixth report contains insights into methodologies for collecting and subsequently disseminating and distributing climate information at a regional scale useful to end users, including policy makers.

Climate information has been aggregated in the form of indicators, which can be climatic variables, such as temperature or precipitation, but also associated extremes or more. These climate indicators have been chosen as very important for planning / adaptation and assessment of climate risk on a local / regional scale. Climate information is therefore available for a number of regions into which continents and ocean areas have been divided.

For example, in the Mediterranean and in Europe, which affect us most directly, extreme high temperature events, estimated on the basis of daily maximum temperatures but also on the duration, frequency and intensity of heat waves, have increased since the 1950s, as well as in the Mediterranean drought phenomena increased, measured on the basis of soil moisture content and water balance. In both cases, the increase is attributable to human activity. According to the climate projections available, these increases will continue into the future, with increasing intensity parallel to the increase in the value of global warming achieved.

This is a machine translation from Italian language of a post published on Start Magazine at the URL https://www.startmag.it/energia/cambiamento-climatico-sesto-rapporto-ipcc/ on Mon, 09 Aug 2021 08:46:12 +0000.