Net Zero, Carbon Sequestration Part Of Solution
Human influence has warmed the climate at a an unprecedented rate. Climate change is already affecting many weather and climate extremes in every region across the globe, including heat waves, droughts, heavy precipitation, and tropical cyclones.
The first IPCC report, released in 1990, concluded that human-caused climate change would soon become evident, but could not yet confirm that it was already happening. Today, evidence is overwhelming that human influence has warmed the climate at a rate that is unprecedented in the last 2000 years. Climate change is affecting many weather and climate extremes in every region across the globe.
With more information and better climate models, we understand more about how the atmosphere interacts with the biosphere. Computer climate simulations have improved dramatically, incorporating many more natural processes and providing projections at much higher resolutions. Since 1990, new technology collects data in the air, on land, at sea and from outer space.
Global surface temperature is fundamental to characterizing and understanding global climate change, including Earth’s energy budget. A rich variety of geological evidence shows that temperature has changed throughout Earth’s history. A variety of natural archives from around the planet, such as ocean and lake sediments, glacier ice and tree rings, shows that there were times in the past when the planet was cooler, and times when it was warmer.
Many aspects of the biosphere are changing. Ecosystems are collapsing. Over the last century, many land species have moved toward the poles and to higher elevations to escape the rising temperatures. Marine species are changing their ranges and migration patterns.
The scale of recent changes across the climate system as a whole and the present state of many aspects of the climate system are unprecedented over many centuries. Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred.
Global surface temperature will increase until at least the mid-century under all emissions scenarios considered. Global warming of 1.5°C and 2°C will be exceeded during the 21st century unless deep reductions in CO2 and other greenhouse gas emissions occur in the coming decades.
Many changes in the climate system become larger in direct relation to increasing global warming. They include increases in the frequency and intensity of hot extremes, marine heat waves, and heavy precipitation, agricultural and ecological droughts in some regions, and proportion of intense tropical storms, as well as reductions in Arctic sea ice, snow cover and permafrost.
With every increment of global warming, changes get larger in regional mean temperature, precipitation and soil moisture. Projected changes in extremes are larger in frequency and intensity with every additional increment of global warming.
Continued global warming is projected to further intensify the global water cycle, including its variability, global monsoon precipitation and the severity of wet and dry events.
Reducing emissions of carbon dioxide (CO2) – the most important greenhouse gas emitted by human activities – would slow down the rate of increase in atmospheric CO2 concentration. However, concentrations would only begin to decrease when net emissions approach zero, that is, when most or all of the CO2 emitted into the atmosphere each year is removed by natural and human processes
Anthropogenic CO2 removal leading to global net negative emissions would lower the atmospheric CO2 concentration and reverse surface ocean acidification (high confidence). Anthropogenic CO2 removals and emissions are partially compensated by CO2 release and uptake respectively, from or to land and ocean carbon pools. CDR would lower atmospheric CO2 by an amount approximately equal to the increase from an anthropogenic emission of the same magnitude. The atmospheric CO2 decrease from anthropogenic CO2 removals could be up to 10 percent less than the atmospheric CO2 increase from an equal amount of CO2 emissions.
If global net negative CO2 emissions are achieved and sustained, the global CO2-induced surface temperature increase would be gradually reversed but other climate changes would continue in their current direction for decades to millennia (high confidence). For instance, it would take several centuries to millennia for global mean sea level to reverse course even under large net negative CO2 emissions.
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