Two papers issued in 2017 have changed thinking about the sea rise projections for the rest of the century from climate change. Here are brief discussions.
NASA’s Sea Level Change Portal site says “Greenland glacier melt speeds East Coast sea level rise”. An analysis of NASA’s satellite survey data shows that the way Greenland’s land ice melts will determine how the Atlantic Ocean will rise over the rest of the century. Quoting from the website “Gravity is putting its thumb on the scale of sea level rise along the U.S. East Coast,
The research for this paper used data from NASA’s GRACE (the twin Gravity Recovery and Climate Experiment) satellites one of the best ways to tell what the impact of the ice mass loss in Greenland and Antarctica is to measure what is going on with the masses in Greenland and Antarctica the paper said. “That makes sense, but the idea that we can look on land to tell us what is happening in the ocean may be counterintuitive to some people.”
Scientific American in their article “Seas Do Not Rise Evenly—It Matters Which Glaciers Melt” that while land-based glacier melt has long been understood as a contributor to sea rise it now depends on where and how quickly it’s happening. “New research predicts how coastlines around the world will be affected by ice melt in different places”.
As the article says it’s a mistake to think of the oceans as a big bathtub. There are many other factors that affect where seawater goes. You probably would be surprised to know that large land glaciers attract sea water simply by their size and the gravitational pull they exert. As theses glaciers melt the water will go elsewhere and its mass was tracked by the satellites. Other factors that can affect seal level include local currents and changes in the sea floor topography as the heavy mass melts away.
Just as we’re getting our heads around this, the journal Nature publishes word of a recent paper (December 6, 2017): “Greater future global warming is inferred from Earth’s recent energy budget”. What is the earth’s energy budget? You may remember learning in middle or elementary school about the “Water cycle” consisting basically of rainfall from, collection, runoff into the ocean or lakes and evaporation back into clouds. The earth’s energy comes exclusively from the sun and its journey as shown in this diagram is much more complicated.
An article by Rebecca Lindsey published in 2009 is a great explanation based published in on NASA’s Earth Observatory website “Climate and Earth’s Energy Budget” is a great explanation. I’ll be quoting liberally from it.
Globally, over the course of the year, the Earth system—land surfaces, oceans, and atmosphere—absorbs an average of about 240 watts of solar power per square meter (about 10 square feet), picture 150 and 75 watt light bulbs shining together.). The absorbed sunlight drives photosynthesis, fuels evaporation, melts snow and ice, and warms the Earth.
The atmosphere and ocean work to even out solar heating imbalances, cold water flowing to warm, through evaporation of surface water, convection, rainfall, winds, and ocean circulation. This is known as Earth’s heat engine.
The climate’s heat engine must not only redistribute solar heat from the equator toward the poles, but also from the Earth’s surface and lower atmosphere back to space. Otherwise, Earth would endlessly heat up. Earth’s temperature doesn’t infinitely rise because the surface and the atmosphere are simultaneously radiating heat to space. This net flow of energy into and out of the Earth system is Earth’s energy budget.
How do the greenhouse gases work in this system? When greenhouse gas molecules absorb thermal infrared energy their temperature rises. Like coals from a fire that are warm but not glowing, greenhouse gases then radiate an increased amount of thermal infrared energy in all directions. Some of it spreads downward and ultimately comes back into contact with the earth’s surface, where it is absorbed. The temperature of the surface becomes warmer than it would be if it were heated only by direct solar heating. This supplemental heating of the Earth’s surface by the atmosphere is the natural greenhouse effect.
The natural greenhouse effect raises the Earth’s surface temperature to about 59 degrees Fahrenheit on average—more than 86 degrees warmer than it would be if it didn’t have an atmosphere so without a greenhouse effect the world might be a barren rock. The problem is that as the amount of greenhouse gases (carbon, methane water vapor) in the atmosphere increases more infrared heat it radiated back to the ground.
Here is the end of the article abstract published in Nature.
“When we compare the model projections with observations, we obtain greater means and narrower ranges of future global warming across the major scenarios, in general. In particular, we find that the observationally informed warming projection for the end of the twenty-first century for the steepest scenario is about 15 per cent warmer (+33 degrees Fahrenheit ) with a reduction of about a third in the two-standard-deviation (meaning more accurate): relative to the raw model projections reported by the Intergovernmental Panel on Climate Change. Our results suggest that achieving any given global temperature stabilization target will require steeper greenhouse gas emissions reductions than previously calculated.””
This is the initial publication and while I suspect that Nature subjected it to some peer review there will be much more.
Regardless of the temperature projections the concern about sea rise is affecting big and small populations, from the scenic stop of Half Moon Bay located along US 1 on the way from Los Angeles to San Francisco, Florida, New York City and US Military bases worldwide there is an increasingly intense conversation about addressing it. My next blog will be about them.
