Summary

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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Past and Future Melts

On the Science Briefs page of the NASA GISS website about a year ago, Dr. Vivien Gornitz posted Sea Level Rise, After the Ice Melted and Today, a succinct article on the sea rises that occurred as the last ice age was ending, from 23 to 3 kiloyears ago. A chart shows meltwater pulses mwp-1Ao, mwp-1A, mwp-1B and mwp-1C, and the text explains research into the sources and sea rise rates of each pulse. None had an average rise rate much greater than 3 meters per century, but occasional centuries did experience rises faster than the average for whatever pulse was then underway.

Transitions from glacial to interglacial periods had more ice vulnerable to rapid melting than our planet has today. Therefore that average meltwater pulse rate of 3m per century, with some lags and surges, is probably the most severe we can plausibly expect for the real near future and succeeding centuries = even if the climate change causing the melt is faster than the end of the last glacial was.

In choosing an average rise rate for our Meltwater fictional geochronology, paleoclimate evidence would suggest the 3m figure as a realistic upper bracket, just as 1.6m is a likely lower bracket.

A later “molten” civilization at high latitudes, ideally after all the perennial polar ice has melted, is our vantage point for any retrospective discourse. However, the further into the future we set this viewpoint civilization, the harder that civilization will be for us to describe and our readers to understand. A realistic upper-bracket sea rise rate means that some 3 kiloyears would need to elapse before the polar ice is gone. A rate between the brackets would require an even longer interval. So I suppose we need to ask: Should our dramatic need for a less remote and more intelligible viewpoint civ trump realism, leading us to posit an average rise rate greater than 3m per century? My tentative answer: No. The sci-fi challenge of narrative realism, so often shirked, is well worth facing. What do you think?

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Watersheds and Mapping

Depending on English dialect, a watershed can mean either all the land area that belongs to the same drainage basin or a boundary that divides drainage basins. The World Conservation Union, also known as the IUCN or International Union for the Conservation of Nature and Natural Resources, maintains an online atlas of watershed maps:

Water Resources eAtlas - Watersheds of the World
Water Resources eAtlas - Global Primary Watersheds Map

Although transient by the timescale of geology, watersheds endure longer than the jurisdictional boundaries of human polities like states, provinces and nations. Persistence and predictability make watershed boundaries more suitable than political boundaries for mapping the Meltwater geochronology.

By their effects on rainfall and agricultural zone location, climate change and sea change are expected to drive rapid, massive migrations and also probably wars of invasion. Surely this turmoil will make political jurisdictions more transient, less predictable and less empirically evident than they’ve been in recent generations.

We, who collaborate to create that fictional future, must learn the way watersheds divide the continents and islands, memorize the shapes of drainage basins and name all the lands after the rivers, lakes and courses where their waters run. Of course we will have to include the desert and coastal basins that the IUCN omits. Every atlas, globe and puzzle we publish can deepen this watershed world view.

Using map colors to distinguish drainage basins instead of nation-states, we can develop legends, methods and conventions that use color mixing and shading within each watershed to show its tributary basins, wetlands and regions covered in summer by ice or snow. We can also inscribe some of our cartographic works with multiple coastlines showing sea-level highstands at different dates in our geochronology, the innermost and highest being dated after the polar ice is gone.

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Marine Isotope Stage 5e

High rates of sea-level rise during the last interglacial period : Abstract : Nature Geoscience
Article : Nature Geoscience
Interview : Scitizen.com

Nature Geoscience has published an online Letter by E.J. Rohling, K. Grant, Ch. Hemleben, M. Siddall, B.A.A. Hoogakker, M. Bolshaw & M. Kucera. Their Letter concerns Marine Isotope Stage 5e, roughly from 124 thru 119 kiloyears ago, during the Eemian or last interglacial period.

In the near future humanity’s unburied carbon emissions are expected to raise global mean temperatures a minimum of 2 Celsius degrees. MIS-5e is the most recent period when our planet was already interglacial in climate, warmed comparably, and underwent changes in sea level.

Calibrating coral data with stable oxygen isotope measurements of central Red Sea sediment cores for “tight stratigraphic control” of the relative ages of core features, Rohling et al. were able to chart the sea rise rates and levels that occurred through MIS-5e. Their average rise rate finding was 1.6 meters per century, occasionally spiking to at least 2.5m per century. Detailed stratigraphic descriptions of coastal/reef architecture enabled Rohling et al. to postulate a +5m sea-level highstand 123 kyr ago, a +9m highstand 121.5 kyr ago, a lesser highstand 119.5 kyr ago, and sea-level drops in between them.

Rohling et al. equate this 1.6m rise rate with melting one Greenland-sized ice sheet every four centuries = just about double the highest rate predicted for the coming century by the recent Fourth Assessment Report of the Intergovernmental Panel on Climate Change. If the melts and highstands of our near future and those of MIS-5e are similar enough, these Rohling et al. findings will have joined a growing body of new indications that polar melt and sea rise may be speedier than the IPCC AR4 predicted.

So how similar will MIS-5e be to our future? Rohling et al. have presented the first detailed information on sea rise rates due to fluctuations within an interglacial. Previous work had focused instead on the sea rise or fall rates due to the transitions between glacial and interglacial periods; such transitional rates can top 5m per century. But the cause of MIS-5e warmth was orbital forcing by insolation, whereas the warming predicted for present and future comes from rapid atmospheric increase of carbon dioxide and other heat-holding gases. This disparity in cause, as pointed out by Rohling et al., could yield some divergent results: “MIS-5e ice-volume responses may have differed in detail from future responses.”

The MIS-5e average sea rise rate of 1.6 meters per century, if duplicated in the real near future, would seriously damage coastal cities and ecosystems. Yet, because today’s Earth has more ice to melt and faster warming to melt it than the Eemian Earth had, it may be the slowest average we can plausibly expect for the next hundred years and many more centuries to come. I think we have to treat that 1.6m figure as our lower bracket when we try to choose a rise rate for the Meltwater fictional geochronology.

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