Research Results
Storms in the Future: Changes in Intensity, Cloudiness, Rainfall and Economic Costs
Title | Introduction | Methods | Results 1 | Results 2 | Results 3 | Discussion
Introduction
1998 was a record-breaking year. It was the warmest year ever experienced during the time that humans have been measuring temperatures, the highest global average surface temperature in almost three hundred years. The following year, 1999 was the sixth warmest year during the same period.1 The evidence shows that our world is in the midst of a period of global warming, even if the debate continues as to the exact causes of the warming. Is the warming just part of the earths natural cycle? Is it the result of anthropogenic contributions? Whatever the cause, the average temperature of the world has increased by 0.5 to 0.7°C over the past century. 2 , and is predicted to rise by as much as another 3 to 5°C over the next 100 years.3, 4 Should we be concerned about the current trend? The world has cooled and warmed by similar amounts in the past as geological records of the various ice ages show. During an ice age the average temperature of the Earth can drop some 5 to 7°C below the current average temperature, covering up to 29% of the earths surface in glaciers. This observation alone portends the enormity of the environmental transformations that could result from such changes in temperature. What makes the current warming period of even greater concern is the rate at which this warming is occurring - at no time in the past has the average temperature of the Earth been observed to change as quickly as it is currently changing.
How will the Earth system react to such rapid changes? With such a large system, with so many complexities, no one can be certain as to exactly what may happen. Both positive and negative impacts of continued global warming have been predicted. Growing seasons may become longer in some areas, a benefit for agriculture, but also influencing the habitats of naturally growing plants. Warmer winters would mean lowers heating bills for homes and businesses, while warmer summers could increase costs for cooling. Ocean levels are expected to rise, endangering costal communities. Infectious diseases may spread more rapidly. Exactly how will humanity be affected by the changes within which it finds itself engulfed? How can we prepare?
1998 also saw the breaking of a second record. In that year insurance companies in the United States paid ten billion dollars in claims for storm related damages the most ever paid.5 The highest temperatures and the most expensive storm damages occurred in the same year. Could there be some connection between global warming and the storms that produce these damages? Climate researchers have long argued that global warming should have some impact upon the storms of the world, particularly the mid-latitude storms of the Northern Hemisphere. These storms are of critical interest, as not only do they affect the part of the world where the majority of the worlds population lives, but they are also the major producers of clouds on the planet. From the clouds comes the precipitation in the form of rain, snow or ice that causes most of the damages associated with storms.
Midlatitude storms result from the difference in heating of the air at the earths equator and its poles caused by the earths spherical shape. Due to this shape, the tropics absorb more energy than the poles. The warmer air of the tropics tends to rise and flow towards the poles. The rotation of the earth then brings the Coriolis Effect into play, causing these air masses to be deflected to the east, which in turn produces the jet-stream. The jet stream is a current of air high in the atmosphere, flowing from West to East across the Northern Hemisphere. The flow of the jet stream is not smooth; disturbances and eddies form within it, causing the cold air and the warm air to intermix. These disturbances are the midlatitude storms. Where the warm and cold air intermingle, low atmospheric pressures are produced, and the warmer, less dense air is lifted up into the troposphere. As the air rises, its temperature decreases, and it can no longer hold the water vapor it contained at the surface. This water vapor begins to condense around aerosols and other small particles, forming droplets of liquid water (and sometimes solid ice), suspended in the air. These suspended water droplets form the clouds, and eventually the mass of suspended water becomes so large that precipitation in its various forms occurs.
The connection between global warming and midlatitude storms lies in the temperature difference between the poles and the equator. This temperature difference behaves much like the potential difference across an electric battery, the greater the difference, the easier it is for energy to flow between the end points. As global warming continues, the temperature difference between the poles and the equator is expected to decrease, making it harder for energy to flow. The poles will warm more quickly, while the already warm tropics will experience small increases, resulting in a smaller temperature difference. This in turn should produce a less energetic jet stream, with fewer disturbances within it. The expectation is that global warming will cause a reduction in the number of midlatitude storms.
There is however, an additional factor to consider. Under continued global warming, the average surface temperature of the earth will increase. Warmer air at the surface will be able to hold more water vapor. When this air is lifted into the atmosphere, there will be more water available to form clouds and precipitation. So even though there may be fewer midlatitude storms in the future, these storms may produce more optically thick clouds and more damage causing precipitation. (Optical thickness is a measure of the total water within a cloud. An optically thick cloud contains a great deal of water and suspended particles, and reflects most of the sunlight hitting it from above. Such a cloud appears dark from below.)
An almost hidden, third factor is the potential of clouds to reduce or enhance the global warming that is occurring. Lower, optically thicker clouds will reflect more solar energy back into space, and have an overall cooling effect. Higher, optically thinner clouds will allow most of this solar energy to pass through to the earths surface, but will then absorb and reradiate some of the infrared energy released by the earths surface, producing an additional warming. Thus, the exact nature of the clouds that will be produced by the storms of the future is of great importance to the climate scientists as they try to predict the magnitude of future global warming.
In our attempt to describe the midlatitude storms of the future and their possible effects upon the billions of humans living in their paths, our research group has taken a multifaceted approach to understanding the characteristics and impacts of these storms. Three teams were created, each with a different focus. One team has concentrated on describing the frequencies and intensities of the storms that may occur under continued global warming. A second team was involved in determing the properties of the clouds that may be associated with these future storms, and a third team was involved with determing the economic impact that these storms may have. Each team used one or two approaches to carry out its investigation.
The first approach, the proxy method, used existing records of past storms, their cloud properties and the damages they have produced to find proxies for describing future changes. The assumption here is that global warming has been occurring for at least the past one hundred years. By looking for trends and making comparisons between extreme cases within the existing data, we hoped to be able to extrapolate future conditions of storms, their clouds and the damages caused by them.
The second approach, the Climate Model, involved the use of the Goddard Institute for Space Studies (GISS) General Circulation Model (GCM) to try to predict the characteristics of future storms. The GCM is a very large, complex computer program containing the equations describing a number of the physical and chemical processes that occur in the world. Initial conditions derived from actual observations are used as the starting point. The GCM is then allowed to run for a number of simulated years, and the output is in the form of values of the conditions at the end of the run. To predict the characteristics of storms after years of global warming, the GCM is run under two sets of conditions. One run is under control conditions, taking the current state of the world and allowing the model to run without any other outside influences. The second run uses the same initial conditions, but introduces the effect of doubling the amount of carbon dioxide in the atmosphere. The final conditions of these two runs can then be compared to see what the model predicts about the characteristics of storms in the event of continued global warming. We can then compare the GCMs predictions to the characteristics of future storms that we derived from past data trends. By this combination of techniques we hope to be able to produce a description of the storm of the future, its clouds and the potential damage it may inflict.
References
1. Hansen, J. (1999), Goddard Institute for Space Studies Website, Global Temperature Trends: 1999 Summation
2. Hansen, J. and Lebedeff, S., Global Trends of Measured Surface Air Temperature, Journal of Geophysical Research, 92,13,345 13,372, 1987
3. Hansen, J., I. Fung, A. Lacis, D. Rind, S. Lebedeff, R. Ruedy, G. Russell, and P. Stone 1988. Global climate changes as forecast by Goddard Institute for Space Studies three-dimensional model, J. Geophys. Res. 93, 9341-9364.
4. Hadley Centre Model Report (1998). Climate Change and its Impacts
5. Property Claims Service, Annual Summary for 1998, 545 Washington Boulevard, Jersey City, N.J. 07310-1686
Title | Introduction | Methods | Results 1 | Results 2 | Results 3 | Discussion
