The Truth About Arctic and Greenland Ice
Posted by Jeff Id on May 27, 2009
I’ve been working on another post on ice area last night. In the meantime Dr. Weinstein has another one for us.
The Truth About Arctic and Greenland Ice
Leonard Weinstein, ScD
May 21, 2009
There is an interesting story going around that Anthropogenic Global Warming (AGW) is resulting in unusual melting of the polar and near polar ice caps, especially the Arctic sea ice and Greenland ice cap, and this is going to contribute to the Earth’s problems in a big way (flooding, feedback temperature increase, etc.). In order to understand the issue, a few simple facts and recent observations need to be shown. The following discussion is restricted to the Arctic and Greenland, since these are the main regions of contention. It should be noted that the Antarctic is presently cooling (and has been for several years) and sea ice extent is expanding.
We first need to examine the external energy balance for the Arctic. Due to the axial tilt of the Earth, the Arctic is in full dark about half of the year, and in partial to full Sunlight about half of the year. The maximum Sun angle at the North Pole is about 24 degrees above the horizon. This angle only occurs for a relatively short time, and smaller angles occur most of the daylight time. The maximum Solar insolation from this (due to the angle and atmospheric absorption) is about 400 W/m2. The high reflectivity of clean snow (always present on ice) results in only about 40 W/m2 being absorbed into the ice. The maximum air temperature near the surface is just a small amount above freezing, so the maximum thermal heat transfer from air to ice is generally just a few 10’s of W/m2. The ice (or snow) gray-body emissivity (about 0.9) is much higher than the low absorption (about 0.1) at the short wavelengths of Sunlight, so the reemitted long wavelength radiation is about 280 W/m2. The result is that solid ice cannot normally melt from Solar radiation plus air warming from the top, even at peak summer. The rest of the year has even less energy input, so ice is strongly cooled all year long.
The actual cause of the significant melting of summer ice has been shown to not be possible from the top. However, there is considerable summer melting. It is clear from the physics that the summer melting has to have been caused by water flowing under the ice. The water flows from lower latitudes, so has a higher temperature than the ice. If the water is warm enough it melts the ice from below. However, if the ice is cold enough and the water cool enough, this flow will freeze and add thickness of solid ice to the underside. This is the source of new solid ice. Snow on the top also adds to the thickness, but is not solid ice.
The summer melting can result in some Arctic open water. Open water can absorb much more of the Solar insolation than ice or snow, but even at the maximum summer level, absorbs only about 350 W/m2 near the pole. The water emissivity is slightly higher than ice, and radiates about 300 W/m2. These result in a maximum excess of absorption in open water of only about 50 W/m2 for a very short part of the peak of summer, and a large net cooling over the full year. Thus to claim that a temporary full melting of Arctic ice (from underneath) will keep the ice from reforming is incorrect based on Solar insolation and reasonable air temperature variations.
The following figure is show as an example of the very rapid temperature rise experienced at the Artic in recent years. This is supposed to prove the model predictions of unusual temperature rise rates are valid, and that we are heading for big problems:
The figure shows a rise rate about 0.25C per decade. This looks scary. However if we look at records back to 1880, we get a different story altogether:
This longer time scale gives about 0.09C per decade if we use the starting and stopping points. However, it is clear that a straight line fit is a ridicules choice, as the temperature actually went up and down. In fact, the highest level occurred around 1940, not the present. It is also true that the temperature has been flat for several years after 2002, and has been falling for the last 2 or so years. The largest jump in temperature occurred from 1915 to 1940. This period predated most of the recent CO2 increase, and even the AGW advocates agree this period was driven by natural forces, not CO2. This demolishes the significance of the claim of the recent rise as proving anything.
The argument for the part of the Greenland icecap that is fully on land and at reasonable altitude has an even stronger argument as to why it will not melt. There is no water to melt the ice from below, and the cooling always exceeds the warming for solid ice at reasonable altitude. Since Greenland is at lower latitude than the pole, the Solar insolation can be significantly higher. If a strong enough warmer wind blows in from the sea, the sea ice and lower altitude edge of the Greenland ice sheet may melt, and has melted many times before (why do you think it is called Greenland). Ice melting at the very edge has led to scare scenes of massive melting, but it cannot happen at the higher altitudes (where almost all of the ice volume is located) at temperature variations that are happening, or that are even projected to occur by the scare models. The following is a temperature record over the last 11,000 years made from a typical ice core from the peak of the Greenland ice cap.
The temperature variations are shown relative to the temperature during 2000. The temperature has been as much as 2C higher than at present, and the last several years have a dropping temperature. The zero line actually corresponds to –30C, so even a temperature rise of 10C or even 20C would not even start to melt the ice.
The result is a clear demonstration that the present models and scare claims are not valid, and that using a short selected time history can give a very misleading indication of longer trends.