Hot Sea Running

17 08 2009

Guest Post from Dan Satterfield

A lot of tropical news this week. The 2009 hurricane season in the Atlantic has stirred to life quickly with two (Update Sunday: 3 !) tropical storms forming on Saturday. It’s not at all unusual to have little hurricane activity until August. The season runs from June 1st to November 30, but the prime season is from Aug, 1st to mid September. American forecasters have an old saying that there will almost always be a hurricane on the weather maps when Labour Day arrives.

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From NOAA/NCDC. The bigger the dot the more the temperature was warmer or colder than normal.

These storms form in very warm ocean. The National Climate Data Center (NOAA) released the July global land and ocean temperatures on Saturday. Ocean temps were the warmest on record for July. The land and ocean temps were the 5th warmest on the instrumental record. This follows June 2009 which also came in as warmest.

Another interesting bit of tropical news this week is a new paper published in Nature on hurricanes of the past. One of the great debates in science right now is the question of whether climate change will bring more hurricanes or fewer. The debate has raged between two opposing groups. Kerry Emanuel of MIT has produced interesting evidence that we have seen an increase in hurricanes already due to the warming of the past 50 years.

Chris Landsea of NOAA has produced evidence that we are just detecting more tropical storms, and that there has not been an increase. I had a chance a couple of years ago to hear both of them present at the AMS meeting in San Antonio. I left with the firm conviction that the question remains open. Understand here, that this debate is not about climate change in general.Despite what you read on the Internet, science has moved on from that.

One thing that does seem very certain now is that hurricanes in the warmer world of late this century, will be wetter. Perhaps considerably wetter. The kind of catastrophic flooding we saw in Taiwan this past week, will likely be more common in the future.

Why you ask? Water vapour.

GOES Image of Tropical Storm Bill Early Sunday. from NASA MSFC
GOES Image of Tropical Storm Bill Early Sunday. from NASA MSFC

If the average temperature of the air over the oceans rises 1 degree F, the air can hold 4% more water. (This is one reason why more snow is likely in Antarctica as it warms, not less. A 3C rise in temp. by late this century would bring an increase of around 22% in the amount of water held in the atmosphere! (You won’t see that bit of science on these junk science sites)

Sea surface temperatures are a major factor in hurricane formation. If the sea surface temperature is below about 27C then hurricanes are not likely. Upper level wind shear and atmospheric water vapour are other important ingredients.

Other factors like wind shear in the upper atmosphere act to inhibit hurricanes. The El Nino that develops every 4-7 years in the Pacific, increases the wind shear over the Atlantic, and we usually see fewer storms. Will there be more wind shear in a warmer world? Possibly. Conditions could combine to produce about the same number of storms in the future. (Much wetter ones though)

Micheal Mann of Penn State University is the lead author of a fascinating paper in this weeks NATURE. His team used soil/silt cores in a series of locations to estimate past hurricanes. If a hurricane hits a coastline, the overwash of sea water will leave a deposit that can be identified in the cores. They used these sediment cores to estimate hurricane activity over the last 1500 years. In addition, they used a statistical model that factored in variables like sea surface temperature to estimate storms as well.

Reconstruction of landfalling Atlantic hurricanes. Nature 460, 880-883 (13 August 2009) | doi:10.1038/nature08219;   Atlantic hurricanes and climate over the past 1,500 years  Michael E. Mann, Jonathan D. Woodruff2 et al
Reconstruction of landfalling Atlantic hurricanes. Nature 460, 880-883 (13 August 2009) | doi:10.1038/nature08219; Atlantic hurricanes and climate over the past 1,500 years Michael E. Mann, Jonathan D. Woodruff2 et al

They found that during a period of rather warm Atlantic Ocean water around 1000 years ago, we saw as many hurricanes as we have over the past 15 years. This is a good confirmation that warmer seas, do give more hurricanes and perhaps more intense ones.

Chris Landsea of NOAA argues that the increase in storms over the past century is just an artifact of spotting them more easily with satellites and aircraft. One thing seems likely here, the hurricanes did increase in the past during a period of warmer oceans.

Whether or not a warmer world caused by human means, instead of natural ones, will do the same is still open for debate. The science, however, might just be beginning to tilt in favor of Mann and Emanuel.

Either way, with sea level now rising 3mm per year, and increasing, future hurricanes, will be wetter and cause more destruction. The current thinking is the IPCC will be adjusting their forecast of sea level rise up considerably in the next report.

This back and forth in the peer reviewed literature is how science advances. When we can answer the question of hurricanes in a warmer world, we will have gleamed another piece of fundamental knowledge of how are planet works.

I end with a book recommendation. Kerry Emanuel of MIT is one of the leading experts on hurricanes. He has written a fabulous book called Divine Wind. It combines poetry and science. It’s one of the best general audience  science books ever written.

Note this is a dual post- I wrote it as a guest post on Skywarn 256’s Weather Blog as well.

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A Synopsis on Climate Change

15 08 2009

There has been skepticism during the entire lifetime of the theoretical atmospheric anomaly called “Global Warming”. Global Warming is a term coined to describe the unnatural rise of the mean low-level atmosphere temperature over a period of time called climate. Global Warming has also been described as Climate Change although it is not a deserved alias as the earth’s climate often changes in temperature over long periods of time (see ice ages and medieval warming). As such, Global Warming should have been coined as the 21st century Global Warming Trend instead of its current names.

Cycle of Greenhouse Gases

The evidence of Global Warming has seemed to pile-up over the time span of its coined existence. This could be due to the fact that more investigations into the global climate heating has resulted in both expected and unexpected evidence and it could be a result of ongoing changes that take place in real time such as the breaking off and thinning of glaciers. Some of the evidence already observed include a research study by various scientists and reported by the Intergovernmental Panel on Climate Change (IPCC) include a global mean temperature increase of 0.74 ± 0.18 °C (1.33 ± 0.32 °F) over the period of the last century although it seems variations in solar radiation and volcanic activity was the primary contributors before the pre-industrial times before 1950.

Temperature Changes
It is forecasted by the IPCC that the global mean temperature could increase yet another 1.1 to 6.4 °C (2.0 to 11.5 °F) by 2100. The uncertainty in the predicted temperature increases is partially due to the fact that different models have forecasted different amounts of chemicals such as Carbon Dioxide in the atmosphere during varying spans of time. The prediction of 2 °F is a conservative guess but the 11.5 °F increase is also quite possible and would be, of course, the worst case scenario.

Temperature History

The NASA Goddard Space Institute estimated that 2005 was the warmest year globally since dependable and accurate modern satellite temperature monitoring began, exceeding the previous record established in 1998 by only a few hundredths of a degree. The high temperatures recorded in 1998 is thought to be a result of an unusually strong El Niño event – the strongest in over a century.

Since global temperatures have been monitored and recorded, various global locations seem to heat faster than others such as the difference in ocean temperatures relative to land-based atmosphere temperatures. Ocean temperatures rise approximately 0.13 °C relative to land-based atmosphere temperatures which rise an average of 0.25 °C during the course of a decade. Many factors contribute to the difference in temperature increases including the ocean having a vast depth and spread in which temperature is required to increase as well as the effect of evaporation on the air above the ocean. Liquids warm and cool much slower than the air, being more dense, thus the difference in temperature fluctuations. Also, the north hemisphere would warm much faster than the southern hemisphere mainly due to the fact that the northern hemisphere has more land area than does the south. With upper air currents in combination with the difference in temperature, the polar regions would heat much faster than regions closer to the equator, thus the rapid warming and thinning of the polar ice caps in the Arctic and Antarctic Circles. Due to the heat-retaining capacity of the oceans as well as the lifespan of Carbon Dioxide, even if all emissions were to cease the global temperature would continue to rise well after 2100.

Global Warming Projections

Another area which affects the global mean temperature is the effects of “Greenhouse Gases” originally discovered and coined by Joseph Fourier in 1824 and was first investigated quantitatively by Svante Arrhenius in 1896. “Greenhouse Gases” are gases which emit and absorb infrared radiation in the planets atmosphere and enhance the atmosphere’s ability to withhold heat energy. “Greenhouse Gases” include but are not limited to: Water Vapor, Methane, Carbon Dioxide, Nitrous Oxide and Tropospheric Ozone. Higher concentrations of these gases lead to the planet’s atmosphere retaining more heat than it exerts thus raising the global mean temperature. Since the industrial revolution, global carbon dioxide levels have increased by 36% – ¾ of the increase is suspected to be a direct result of the burning of fossil fuels. Evidence extracted from deep ice pockets suggest that carbon dioxide levels are higher than they have been in the last 650,000 years – additional evidence is believed to indicate that levels are actually higher than they have been in the last 20 million years. Although most of the gases mentioned enhance the planets ability to retain heat, some chemicals known as aerosols which are either released naturally, as is the case with volcanoes, or by human sowing as is the case with some CFCs. These chemicals reflect radiation back into space from the upper atmosphere countering the effects of “Greenhouse Gases”. Although this may have been the case up until now, it seems as if the amount of “Greenhouse Gases” such as carbon dioxide and methane are well exceeding the amount of aerosol in the atmosphere. This may have been the reason that extreme global mean temperature increase was delayed during the latter half of the 20th century and only become urgent from the beginning of the new millennium onward. Methods have also been used by scientists to combat global warming indirectly and directly including the use of Biochar, Geoengineering and the like.

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