Climate Conversations : Earth’s response

climate-noaaClyde Burnett, Peak to Peak.  The universal laws of Nature are independent of politics and much more predictable. The role of CO2 in increased infrared heat trapping is continuing with global warming and climate change.

Much of our weather is due to the large difference in the solar heating between the tropics and the polar regions. We look first at the global warming in the Arctic. Ocean ice albedo, the fraction of sunlight that is reflected away from the planet, is about 60%: water albedo is only about 6% . So the albedo change from the ice melt in the Arctic Ocean is a feedback for Arctic warming and the Arctic warms at twice the rate of the rest of the Earth surface. The 2016 sea ice minimum at the end of summer melt was tied with that in 2007 at 1.6 million square miles. That area has been decreasing at 12% per decade; the ice is predicted to disappear by 2030. We have this additional confirmation of the temperature measurements of global warming.

The Earth’s transport of heat from tropical to polar regions is accomplished by the movement of polar and tropical air masses. We will consider what happens in the troposphere, which is the lower atmosphere up to about 40,000 ft; water vapor and weather are restricted to this region. The vertical structure of cold and warm air masses in this region differ with density and pressure of the cold air mass concentrated at lower altitude. The wind response to the resultant horizontal pressure difference at the top of the troposphere is influenced by the earth’s rotation. This is a deflection of the wind to the right in the Northern Hemisphere with the counterclockwise wind about low pressure at the surface, and with a west-to-east Jet Stream at the top of the troposphere.

Of the greenhouse effect trapped energy, 90% warms the ocean. Earth responds with an increase in the overall atmospheric water vapor by evaporation and changes in storm movements and precipitation. Much of our weather occurs at this interface with the condensation of evaporated water from the tropical air mass. The movement of these storms is guided in direction and speed by the Jet Stream.

Question: How is this changed by global warming?

Answer: The polar mass is not as cold as in the past. The pressure gradient near the tropopause is not so great; the Jet Stream is not so strong and the storms move more slowly, which increases the accumulation of precipitation.  Finally, the mature storms no longer support the pressure conditions for a Jet Stream and these “upper low disturbances” are cut off from Jet Stream guidance, remaining almost stationary with increased accumulation of precipitation.

Question: What does global warming do at the equator?

Answer: Global warming drives a more active Hadley cell. This is a vertical circulation cell first theorized by Hadley in the 18th century. The tropical air is subjected to upward convection with condensation near the equator and forced northward near the top of the troposphere. This air descends near 30o latitude; this subsidence must yield a warm dry stable high pressure area. It is generally credited with causing the Sahara Desert; it is not a factor in daily weather forecasts. With global warming, the Hadley cell circulation is likely to be strengthened with expansion of a dry warm midlatitude air mass.

The recent drought in southeast U.S. is remarkably consistent with such a circulation change. At the surface we have a heat wave and drought; the stable atmosphere has trapped wildfire smoke near the ground. Satellite water vapor observations exhibited a complete absence of upper troposphere water vapor over the entire area that is now replaced by moisture from winter storms.