To repeat: In this series of blog posts, I attempt to give an overall view of the physics/chemistry-based climate science dealing with climate change and today’s global warming. I do so because I can’t find an overall summary such as the one I’m about to try to create. My hope is that readers will understand why this science makes me so alarmed and seemingly so pessimistic. As always, misunderstandings and misstatements are my fault and do not reflect on the science itself.
In this post, we take a look at what climate science has to say about today’s human-caused global warming. This episode of global warming beyond what would be expected from the Milankovitch cycle and underwater volcanism (that is, from a “Goldilocks” steady state that would soon begin to slowly decrease towards an Ice Age) has already taken us to global temperatures not seen for the last 1-5 million years. An additional 1.5 degrees C is already “baked in” – that is, the temperatures have not yet caught up to the atmospheric carbon level, but even with zero carbon emissions from now on, and without some technology that we do not presently have, we will still see this additional increase to a new “semi-steady state”.
The key difference between all previous episodes of global warming and this human-caused one is that for the first time ever, carbon stored in animal and vegetative matter beneath the Earth (including the shallow parts of the oceans) is being brought above ground and burned, injecting into the atmosphere much of the carbon so stored over the last 100 million to billion years of life on Earth. Specifically, this means oil, natural gas, and coal, as well as the tar sands and oil shale that also contain “fossils”. If all of the rest of this “energy reserve” were to be used in the same way over the next 100 years, then atmospheric carbon would probably reach more than 2000 ppm, and possibly as high as 4000 ppm.
As should be clear from my last blog post, the main difference in climate behavior from previous episodes of global warming is that atmospheric carbon injection is happening far faster: about 100 times faster. Thus, parts of the climate process that operate to slow global warming or return to a previous “steady state”, which operate much more slowly, have very little impact on this global warming. More specifically, “weathering” has very little impact, and oceanic ice-creation mechanisms that operate to keep the Arctic filled with sea ice also cannot operate very well.
Let’s be a little more specific about the last point. The Oceans in today’s Earth operate in a great surface/underwater loop or “conveyor belt”. The Gulf Stream’s warm water moves up to a point near Greenland, cooling as it goes. When it reaches that point, it dives down below the surface and begins a journey south to the Antarctic Ocean, and from thence up the Pacific to a point near Alaska and Siberia, where it resurfaces and completes the loop back to the Gulf Stream. This is called a “conveyor belt” because it transmits surface ocean temperature changes to the deep Ocean over a period of about 100 years.
When global warming causes sea ice to melt more at the “dive-down” point, that sea ice is fresher water, and therefore warmer (salt prevents water from freezing until it reaches about 29 degrees F, at which point the salt is expelled from the sea ice). That warmer, fresher water slows or even stops the Gulf Stream from diving down at the dive-down point. That, in turn, slows down or stops the rest of the Gulf Stream if it goes on too long. If it doesn’t, the fresher water, being more easy to freeze, reforms near the dive point, and the “diving down” resumes. In effect, up to a point, this circulation cycle acts to retard or reverse the loss-of-sea-ice albedo effects of global warming. However, the faster the global warming, the less effect this mechanism has.
Climate Effects of Today’s Global WarmingToday’s global warming has and will have (remember, further temperature increases are “baked in”) effects on global climate especially in four ways:
1. Temperatures in the Arctic and Antarctic warm perhaps 5-10 times as much as those nearer the Equator. Also, winter temperatures warm more than summer ones, and night temperatures warm more than day ones. The key effect from this on the Northern Hemisphere is that the temperature differential between Northern Eurasia and Northern America and the Arctic decreases, while weather patterns on both sides of that divide have more energy to stay on the “wrong side”. The initial result is that weather systems on both sides linger longer, and are more extreme. Boston saw almost-record cold last January for long periods of time, as Arctic weather came down and lingered; the Arctic saw several unprecedented warm spells from the south over this New Year, including a 22-hour period where the temperature was above freezing. In the long run, however, the warmth from global warming will dominate the cold from the Arctic: a few million years ago, 360 ppm atmospheric carbon saw a subtropical Arctic.
2. The atmosphere has more energy (heat) and more rain, making for stronger and windier extreme-weather events. It appears that increased incidence of tornadoes and increased top winds in hurricanes are to some extent caused by these temperature increases. Likewise, heavier rain/snow when it occurs and greater wind-driven oceanic “storm surges” onto land are definitely occurring and are effectively caused by global warming.
3. Climate “zones” move poleward, i.e., northward/southward. In particular, subtropical zones with high heat and massive droughts extend northward/southward. In 2050-2070, America/southern Canada (except New England/NY), pretty much all of Europe, the Middle East, India, and 2/3 of China, as well as Australia and Tasmania, are projected to be suffering Dust-Bowl-like droughts, if things go on as they have. This may or may not be true if very strong action is taken that reduces drastically human contributions to atmospheric carbon. Because of the unusual speed of global warming, the majority of ecosystems in these area cannot move northward effectively and are faced with extinction in the next 100 years. Also, a decreased availability of water for farming due to loss of snowpacks and overuse of aquifers combined with the drought conditions places perhaps ½ of all of today’s arable land under threat.
4. Land ice and snow melts exceptionally rapidly. Melting of sea ice only causes slight ocean rise, as ice displaces as much area as cold water; oceanic heat increases (slow to happen, as noted) expand and therefore raise the oceans less than 10%. Land ice and snow melting, however, translates directly into sea-level rise. The key areas here are Greenland, West Antarctica, and East Antarctica. A domino effect in the Arctic, which has already started, removes the sea-ice barriers to increased flow of Greenland glaciers into the oceans surrounding it, leading to a doubling of net land-ice loss there every 10 years. West Antarctica has already begun the same process, especially in the Antarctic Peninsula, and it appears that East Antarctica is doing so as well. Greenland may contribute as much as 10 feet of sea-level rise this century, while West Antarctica may well also contribute that amount. In the longer term (again, this may be “baked in” by a 360-ppm atmospheric carbon level), sea level rise may reach a maximum of 220-240 feet. This would submerge 1/3 of the world’s present arable land in salt water. If we add 30-foot-higher storm surges that “salt” water supplies inland, most of today’s coasts to 50-100 miles inland will be uninhabitable. Thus, for example, in the US, Florida, Louisiana, Alabama, and Mississippi will effectively cease to exist.There are also indirect “feedback loops” related to climate change that make temperature increases per atmospheric-carbon doubling 4 degrees C rather than 2.5 degrees C. The three key effects there are increased albedo due to ice/snow replacement by water/rock/earth, melting of permafrost (which has already begun to occur) that leads to release of permafrost carbon into the air, which in turn increases temperature, and emergence of “black carbon” from the layers of melted ice, which “dirties” and thereby increases the albedo of remaining snow/ice as well as adding carbon to the atmosphere.
Finally, we should note some of the things that do not affect today’s climate change in the medium to long term:
1. Above-water volcanism and “nuclear winter”. These create winter-like conditions in which the temperature drops drastically. In both cases, the particles that create these conditions linger for 1-7 years, but the net effect on underlying climate change is exactly zero: if you double atmospheric carbon during the 1-7-year period after an eruption or nuclear-winter episode, at the end of 7 years a temperature increase of 4 degrees C will be “baked in.”
2. Changes in the amount of cloud cover caused by climate change. Studies have shown that, if anything, these increase temperatures slightly.
3. Aerosol pollution. This is most frequently a side-effect of coal burning, and results in increased “smog”-related airborn particles that decrease temperatures significantly. However, as China is now finding out, aerosol pollution can only counteract increased atmospheric carbon up to a point, after which people suffering aerosol pollution will die. Thus, it now appears extremely likely that overall aerosol pollution will decrease over the next century, “uncovering” the temperature increases that were masked by the pollution increases.
4. Methane emissions will increase sharply, but it now appears that their overall effect will be relatively small.
SummaryWhat worries climate scientists the most about today’s global warming is its unprecedented speed and extent, both of these being the result of humans rapidly and massively extracting and injecting into the atmosphere hundreds of millions of years of sequestered carbon primarily from dead animals and plants. The resulting feedback loops and processes, less checked than ever before by stabilization processes, enhance the immediate temperature effects of the new atmospheric carbon and have reached the point of oceanic saturation where much of the carbon now in the atmosphere will not be “cycled out” for thousands of years.
But there is another key implication of today’s process of global warming. At every stage, the climate effects of doubling atmospheric carbon are 2-10 times greater – including the negative ones. Thus, while storm surges once we enter the 500-1000 ppm atmospheric carbon stage, the frequency of 100-mph storms now equals that of 80- or 90-mph storms in the previous stage; and the damages from 100-mph winds is 10 times that of 80-90-mph winds. To fail to prevent 500 ppm atmospheric carbon is an argument for redoubling our efforts to prevent 1000 ppm atmospheric carbon, not for giving up, because the consequences of failure to prevent each stage get progressively worse.
What is the worst that can happen, and what does it require? According to a recent study by Hansen et al, the “can’t get any worse” scenario happens when we burn a certain amount of today’s fossil fuel reserves within the next 100-200 years:
If we burn all the coal plus a very minor amount of everything else, we reach “worst consequences.”
If we burn all of the oil, 33% of the coal, and none of the gas/tar sands/oil shale we reach “worst consequences”.If we burn 17% of the coal, 50% of the natural gas, and all the tar sands/oil shale/oil, we reach “worst consequences”.
What are the worst consequences? Here’s a brief summary of those:
In Hansen’s worst-consequence world, humans could survive below the mountains during the day outside only for short periods of time during the summer, and there would be few if any places to grow grains.
In my version of Hansen's worst-consequence world, we would try to survive on less than 10 % of today's farmland, less than 10 % of the animal and vegetable species (with disrupted ecosystems), and practically zero edible ocean species, in methane-heavy mosquito-infested peat swamps that must be developed before they can be farmed, in dangerous weather, for thousands of years.My final blog post on this subject will examine certain implications of climate science on effective ways to combat today’s global warming.