One factor that warms our planet is the concentration of carbon dioxide (CO2) gas in its global atmosphere. CO2 is one of several gases that absorb or scatter infra-red photons, mostly from the surface of the Earth, and heat up as their molecules are kinetically excited by the scattering and absorption. This fact of radiation physics was discovered by the likes of J.B.J. Fourier and John Tyndall between 190 and 150 years ago. Heat-absorbing gases are often called greenhouse gases and the warming they cause is often called the greenhouse effect, but these terms are misnomers. Real indoor-gardening greenhouses keep warm by suppressing convection, which excited gases never do. A better phrasing would mention the gas excitement effect due to IR-excitable gases.
One key process that adds carbon dioxide to the atmosphere is the un-burial and combustion of coal, petroleum and natural gas by human industry. These fossil fuels are accessible in sufficient quantity to multiply atmospheric CO2, a calculation published over a century ago by the likes of Arvid Högbom and Svante Arrhenius. The global mean surface temperature increase caused by doubling the atmospheric CO2 concentration is known as the CO2 sensitivity. Temperature measurements, weather observations, paleoclimate core and proxy data, and satellite surveillance together yield a picture of climate that cannot be modeled, reproduced or explained unless the CO2 sensitivity is around 2.3 Celsius or Kelvin degrees, or 4.14° Fahrenheit, at a minimum.
Atmospheric CO2 is rising fast and its isotropic fingerprint agrees with fossil fuel and cement emission rates: human activity is responsible for the current increase.
Compared with its pre-industrial concentration of 280 parts per million, atmospheric CO2 is nearly certain to double within a few decades. To stabilize its concentration at that 560ppm level instead of some higher figure will require rapid, expensive, worldwide, persistent acts of political will without precedent, placing a cost on unburied carbon emissions (as if in constant year-2000 US dollars) approaching $40 per tonne to incentivize the de-carbonization of our energy systems. It cannot be done without massive technological changes like introduction of cellulosic or microbial biofuels, expansion of renewable, solar, hydroelectric, wind, marine energy and nuclear fission power, and equipping fossil fuel powerplant furnaces with CO2 capture and storage adequate for ultra-long-term sequestration. Lifestyle changes will also be required. Pessimistic views of human behavior make timely worldwide accomplishment of all these necessities hard to imagine. Optimism demands that we make the attempt. Even if it can be done we will still get at least a 2.3°C global mean temperature increase because we will still have doubled CO2 and that much sensitivity is dictated by the physics of our climate system.
During the sort of interglacial period that we currently inhabit, if the Eemian example MIS-5e is any guide, 2°C suffices to raise global sea level for the next hundred years and many centuries to come by an average of 1.6 meters, or about 5 feet, per century. That may be the best case that we can, on average, expect. During MIS-5e, some centuries suffered a sea rise rate higher than average, others a lower; a few centuries knew some stability or even a sea level drop.
Average is bad enough to displace a massive proportion of human populations and agriculture by drowning many coastal cities and lands. This rise in sea level will result from polar melt, one among various effects due from global warming. Because our globe is warming at a rate without recent geological precedent, rapid sea rise might come soon.
Of the farmlands and forestlands not swallowed by the oceans, many will be swallowed up by other warming effects, like beetle boom, wildfire, dust bowl drought, desertification and soil erosion. By depleting soil moisture, snowpacks, glaciers, aquifers, wetlands and lakes across many continental interiors, global warming puts fresh water and food supplies at risk. As climate zones move poleward and upslope, agriculture and silviculture must occupy new lands quickly, without expanding IR-excitable gas emissions from plowing and producing fossil petrochemical fertilizers. Agricultural biochar might help. Rain and meltwater must be collected by roofs and pavements, and held upstream by new dams for new reservoirs. Yet the new lakes and new farming we need will speed the loss of territory suffered by many natural habitats, increasing risk to the ecosystem services they provide.
Given this rather grim outlook, which obtains even if decades of emissions-cutting efforts that have yet to commence are globally effective, many people unsurprisingly seek to question the scientific basis for predicting global warming and blaming it on human activity. Yet, of the many objections raised, only a few ever had any apparent claim to scientific merit. They include: Knut Ångstrom’s experiment suggesting that IR-absorption bands were close to saturation and more IR-excitable gases could be emitted with impunity after saturation was achieved; Hubert Lamb’s observation that climate globally cooled from the 1940s through the ’70s in spite of growing unburied carbon emissions; and proposals that oceans and other natural systems could absorb excess carbon dioxide without undue harm. Over the course of the 20th century CE, all such respectable objections were thoroughly answered by peer-reviewed science.
Since then a disreputable campaign of denial has recycled old arguments as if they were never answered and offered new objections with less or no merit. Whether misled by stubgullim or innocently ignorant, many people are susceptible. Having successfully confused much of the media and public, the denialist campaign has temporarily thwarted political action to regulate emissions, but the climate itself and its effects on the oceans will eventually turn the tide of opinion.
Meanwhile, we can employ geographic realism to envision a science-fictional chronology of global warming’s likely consequences. Such is the goal of this blog.
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