Climate Models Improve As Prognosis Worsens
You don’t have to be a climatologist to see the warning signs of global warming and climate change. Not only are the problems on the rise, they are accelerating. Most climate models are wrong because they don’t account for the escalation.
Earth’s climate has always changed naturally, but both the global extent and rate of recent warming are unusual. The recent warming has reversed a slow, long-term cooling trend, and research indicates that global surface temperature is higher now than it has been for millennia.
The signs of climate change are unequivocal at the global scale and are increasingly apparent on regions and communities. The high northern latitudes show the largest temperature increase with clear effects on sea ice and glaciers. The warming in the tropical regions is also apparent because the natural year-to-year variations in temperature there are normally small.
Climate models are important tools for understanding past, present and future climate change. They are sophisticated computer programs that are based on fundamental laws of physics of the atmosphere, ocean, ice, and land.
Climate models have improved and continue to do so, becoming better at capturing complex and small-scale processes and at simulating present-day mean climate conditions. This improvement can be measured by comparing climate simulations against historical observations. Both the current and previous generations of models show that increases in greenhouse gases cause global warming.
As scientists seek to refine our understanding of Earth’s climate system and how it may evolve in coming decades to centuries, past climate states provide a wealth of insights. Data about these past states help to establish the relationship between natural climate drivers and the history of changes in global temperature, global sea levels, the carbon cycle, ocean circulation, and regional climate patterns, including climate extremes. Guided by such data, scientists use Earth system models to identify the chain of events underlying the transitions between past climatic states. For example, nights are warming faster than days, less heat is escaping to space, and the lower atmosphere (troposphere) is warming but the upper atmosphere (stratosphere) has cooled.
We understand climate change better now compared to when the IPCC started. 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 at least the last 2000 years. Human-induced 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.
With much more data and better models, we also understand more about how the atmosphere interacts with the ocean, ice, snow, ecosystems and land surfaces of the Earth. Computer climate simulations have also improved dramatically, incorporating many more natural processes and providing projections at much higher resolutions. Since 1990, large numbers of new instruments have been deployed to collect data in the air, on land, at sea and from outer space.
IPCC’s Sixth Assessment Report (AR6) incorporates subsequent new evidence from climate science, including new and better representation of physical, chemical and biological processes. Although the report is sobering, answers begin with the truth.
Temperature is a key indicator of the overall climate state, and 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. While our confidence in quantifying large-scale temperature changes generally decreases the farther back in time we look, scientists can still identify at least four major differences between the recent warming and those of the past.
- It’s warming almost everywhere.
- It’s warming rapidly.
- Recent warming reversed a long-term global cooling trend.
- It’s been a long time since it’s been this warm.
These conclusions are based on evidence, including direct observations of recent changes in Earth’s climate; analyses of tree rings, ice cores, and other long-term records documenting how the climate has changed in the past; and computer simulations based on the fundamental physics that govern the climate system.
Long-term changes in other variables such as rainfall and some weather and climate extremes have also now become apparent in many regions. It was first noticed that the planet’s land areas were warming in the 1930s. Although increasing atmospheric carbon dioxide concentrations were suggested as part of the explanation, it was not certain at the time whether the observed warming was part of a long-term trend or a natural fluctuation – global warming had not yet become apparent. Since then, observed changes in key indicators point to warming over land areas. Oceans are warming. Changes also are evident over the cryosphere – the portion of the Earth where water is seasonally or continuously frozen as snow or ice.
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.
Warming dominated by past and future CO₂ emissions. Global surface temperature will continue to 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.
Under scenarios with increasing CO2 emissions, the ocean and land carbon sinks are projected to be less effective at slowing the accumulation of CO2 in the atmosphere. The rates of CO2 taken up by the land and oceans are projected to decrease in the second half of the 21st century.
Many changes due to past and future greenhouse gas emissions are irreversible for centuries to millennia, especially changes in the ocean, ice sheets and global sea level.
Variations in solar and volcanic factors partially masked human-caused surface global warming during 1998–2012.
Since AR5, estimates of remaining carbon budgets have been improved by a new methodology first presented in SR1.5, updated evidence, and the integration of results from multiple lines of evidence. A comprehensive range of possible future air pollution controls in scenarios is used to consistently assess the effects of various assumptions on projections of climate and air pollution. A novel development is the ability to ascertain when climate responses to emissions reductions would become discernible above natural climate variability, including internal variability and responses to natural drivers.
From a physical science perspective, limiting human-induced global warming to a specific level requires limiting cumulative CO2 emissions, reaching at least net zero CO2 emissions, along with strong reductions in other greenhouse gas emissions. Strong, rapid and sustained reductions in CH4 emissions would also limit the warming effect resulting from declining aerosol pollution and would improve air quality.
The effects of substantial reductions in carbon dioxide emissions would not be apparent immediately, and the time required to detect the effects would depend on the scale and pace of emissions reductions.
This Report reaffirms with high confidence the AR5 finding that there is a near-linear relationship between cumulative anthropogenic CO2 emissions and the global warming they cause. Each 1000 GtCO2 of cumulative CO2 emissions is assessed to likely cause a 0.27°C to 0.63°C increase in global surface temperature with a best estimate of 0.45°C. This is a narrower range compared to AR5. This quantity is referred to as the transient climate response to cumulative CO2 emissions (TCRE). This relationship implies that reaching net zero anthropogenic CO2 emissions is a requirement to stabilize human-induced global temperature increase at any level, but that limiting global temperature increase to a specific level would imply limiting cumulative CO2 emissions to within a carbon budget.
Estimated remaining carbon budgets are calculated from the beginning of 2020 and extend until global net zero CO2 emissions are reached. They refer to CO2 emissions, while accounting for the global warming effect of non-CO2 emissions.
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 (CDR) 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, depending on the total amount of CDR.
If global net negative CO2 emissions were to be achieved and be 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.
Achieving global net zero CO2 emissions is a requirement for stabilizing CO2-induced global surface temperature increase, with anthropogenic CO2 emissions balanced by anthropogenic removals of CO2.
Reducing the rate of increase in CO2 concentration would slow down global surface warming within a decade. But this reduction in the rate of warming would initially be masked by natural climate variability and might not be detected for a few decades. Detecting whether surface warming has indeed slowed down would be difficult in the years right after emissions reductions begin.
Reductions in GHG emissions also lead to air quality improvements. However, in the near term, even in scenarios with strong reduction of GHGs, as in the low and very low GHG emission scenarios, these improvements are not sufficient in many polluted regions to achieve air quality guidelines specified by the World Health Organization.
In summary, it is only after a few decades of reducing CO2 emissions that we would clearly see global temperatures starting to stabilize. By contrast, short-term reductions in CO2 emissions, such as during the COVID-19 pandemic, do not have detectable effects on either CO2 concentration or global temperature. Only sustained emission reductions over decades would have a widespread effect across the climate system. Access IPCC’s Sixth Assessment Report
To address these challenges, Gary Chandler has developed the following two initiatives:
Sacred Seedlings is a global initiative to support forest conservation, reforestation, urban forestry, carbon capture, sustainable agriculture and wildlife conservation. Sustainable land management is critical to the survival of entire ecosystems.
Greener Cities is a resource for sustainable and resilient cities and communities around the world.