By PATRICK MAYOYO
Increases in greenhouse gases (GHG) concentrations since around 1750 are unequivocally caused by human activities, a new study reveals.
The report, Climate Change 2021 : The Physical Science Basis, says land and ocean have taken up a near-constant proportion (globally about 56% per year) of CO2 emissions from human activities over the past six decades, with regional differences.
“It is unequivocal that human influence has warmed the atmosphere, ocean and land. Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred,” it emphasizes.
The report adds that globally averaged precipitation over land has likely increased since 1950, with a faster rate of increase since the 1980s and it is likely that human influence contributed to the pattern of observed precipitation changes since the mid-20th century, and extremely likely that human influence contributed to the pattern of observed changes in near-surface ocean salinity.
The Intergovernmental Panel on Climate Change (IPCC) study notes that human influence is very likely the main driver of the global retreat of glaciers since the 1990s and the decrease in Arctic sea ice area between 1979–1988 and 2010–2019 (about 40% in September and about 10% in March).
The report says changes in the land biosphere since 1970 are consistent with global warming: climate zones have shifted poleward in both hemispheres, and the growing season has on average lengthened by up to two days per decade since the 1950s in the Northern Hemisphere extratropics.
The 4,000 pages report, released earlier this month, paints a grim future for a world where climate change is “widespread, rapid and intensifying,” and in some cases, irreversible.
“Global mean sea level has risen faster since 1900 than over any preceding century in at least the last 3000 years (high confidence). The global ocean has warmed faster over the past century than since the end of the last deglacial transition (around 11,000 years ago),” the report observes.
Scientists who compiled the report explored different scenarios over the next several decades, including how sea ice cover might change if the United States significantly changes its practices regarding carbon emissions, or if it stays the course.
According to the IPCC report, the Arctic region has warmed at more than twice the global rate over the last 50 years and will continue to do so at a higher rate than the global average. The rapidly-heating waters will impact more than just sea ice cover.
Marine mammals are not the only ones at risk. Other marine wildlife, including fish, may see significant population shifts as warmer waters force fish north.
This is the sixth report from the IPCC, an organization created by the United Nations Environmental Programme (UNEP) and the World Meteorological Organization (WMO) in the 1980s.
The reports are designed for policymakers around the globe to explore the future impacts of climate change in their region. In The IPCC report detailed several aspects of climate change that may impact the Arctic region in the coming years.
The report also detailed that shorelines will continue to retreat and coastal communities may experience “severe coastal flooding” in the future.
“It is virtually certain that hot extremes (including heatwaves) have become more frequent and more intense across most land regions since the 1950s, while cold extremes (including cold waves) have become less frequent and less severe, with high confidence that human-induced climate change is the main driver14 of these changes,” the study adds
It adds that since 1750, increases in CO2 (47%) and methane aka CH4 (56%) concentrations far exceed, and increases in nitrous oxide aka N2O (23%) are similar to, the natural multi-millennial changes between glacial and interglacial periods over at least the past 800,000 years.
The report says global surface temperature has increased faster since 1970 than in any other 50-year period over at least the last 2000 years (high confidence). Temperatures during the most recent decade (2011–2020) exceed those of the most recent multi-century warm period, around 6500 years ago13 [0.2°C to 1°C relative to 1850– 1900.