|CLIMATE IN 1995
The World Meteorological Organisation recently released its "Statement on the status of the global climate in 1995". This is the summary. Also included is an article explaining the importance of tropical rainforests for climatic stability.
The 1995 estimated global mean surface temperature over land and marine areas was the warmest since 1861. The warmth could not be attributed to El Nino/Southern Oscillation (ENSO) since the contrasting equatorial Pacific Ocean surface temperature anomalies were averaged to be near normal for the year. In the North Atlantic, however, sea-surface temperatures were more than 1°C warmer in an area centred on the Azores. Parts of Siberia averaged more than 3°C warmer than the 1961 to 1990 period and many heat-related deaths occurred in both the midwest United States and India during the northern hemisphere summer. As is usual, there were regions where the temperatures were cooler than normal in 1995, including Greenland and the adjacent north-west Atlantic Ocean as well as mid-latitudes of the North Pacific Ocean.
There were many extreme climatic anomalies and weather events in 1995. The most active hurricane season in the Atlantic Ocean since 1933 caused considerable property damage in the Caribbean islands and the south-east coastal areas of the United States. Following prodigious rains in January and February, which caused massive flooding along major continental European rivers, the summer over the same region was of near record heat and, in the United Kingdom particularly, serious precipitation deficiencies caused widespread restrictions on water usage. There were examples of beneficial events, including the return of abundant rains to such widely separated but drought-stricken regions as north-west Africa/Iberian Peninsula, southern Africa and Australia.
Six months after international scientists agreed human activity was having a "discernible" influence on the worlds climate, the report appears to confirm their fears about global warming.
Additionally, the report said the hole in Earths protective ozone layer, which has become a regular feature over the Antarctic in spring, started earlier and lasted longer than in any recorded year. Ozone in the lower stratosphere, at altitudes of between 14 kilometres and 20 kilometres, was almost completely destroyed. The size of the hole, at 22 million square kilometres, almost matched the 1993 record. [The 1993 record was created by the effect of Mt. Pinatubo which no longer contributes to ozone depletion.]
According to Lester Brown, Christopher Flavin, and Hal Kane, writing in The Trends That Are Shaping Our future, "As temperatures were climbing, crop-withering heat waves were shrinking the 1995 world grain harvest, making it the smallest since 1988. This, combined with the soaring worldwide demand for food, dropped carryover stocks of grain for 1996 to 48 days of consumption, the lowest level ever, reports the D.C.-based environmental research organisation. The stage was set for a record rise in grain prices. Ironically, in an era of of space exploration, humanity was suddenly struggling in 1996 with one of the most ancient of challenges - how to make it to the next harvest.
The average global temperature in 1995 reached 15.39 degrees Celsius, breaking the previous mark of 15.38 degrees in 1990. The 10 warmest years in the last 130 have all occurred in the eightiesand nineties. And within these 10, the three warmest years were in the nineties. In 1995, carbon emissions from the burning of fossil fuels reached a record 6.1 billion tonnes. Among other things, this indicates that governments of industrial societies are failing to meet the goal of limiting carbon emissions that was set by the Framework Convention on Climate Change signed at the 1992 Earth Summit.
Agriculture was not the only sector feeling the effects of higher temperatures. As temperatures rise, warmer oceans release more energy into the atmosphere, leading to more intense and violent storms. Worldwide, insurance industry payouts for weather-related damage have climbed from $US16 billion during the eighties to $48 billion thus far during the nineties. The insurance industry is reeling from this dramatic surge in claims. Voicing the fears of many in the industry, Franklin Nutter, president of the Reinsurance Association of America, says, "The insurance business is first in line to be affected by climate change ... it could bankrupt the industry." The report notes that in 1995, the global economy grew by an estimated 3.7 percent, the largest gain since the 4.7 percent growth of 1988. This impressive expansion raised the global output of goods and services per person by 2 percent, but also increased further what had already become unsustainable demands on the earths natural systems and resources - croplands, aquifers, fisheries, rangelands, and forests.
The continuing and increasing destruction of primary forests worldwide is of the cause of the gravest concern for the continuance of life on Earth. No region is under greater threat than South America, and no country has greater responsibilities than Brazil. Noeline Gannaway has prepared the following article based on research and analysis published originally in the Ecologist between 1985 and 1991 - by Peter Bunyard (Vol.15 No.3 1985), Luiz Carlos B. Melion (Vol.19 No.6 1989), and Risto Isomeki (Vol.21 No.1 1991).
The interaction of the rainforest with its environment has consequences that extend far beyond the narrow belt where the forest is found. The earth's hydrological cycle, the transfer of heat from the tropics towards the poles, the chemistry of the atmosphere, and global climate are all influenced by the tropical forest: deforestation is bound to cause changes. Just what those changes are likely to be, cannot as yet be predicted with certainty. What we do know is that the tropical forest is a complete biological system in which every component, from the soil upwards through the canopy to the outer atmosphere, plays its part. A change in one component is therefore likely to ripple through the system. For instance, the compaction of soil, brought about through clearing the forest with heavy machinery, alters run off, destroys the relationship between soil organisms and disturbs the energy balances of the system with ultimate effects on climate. The scale of these effects depends on the extent of rainforest destruction.
Amazonia and Climate Stability.
Along the equatorial belt there are three regions of ascending air motion: the `Maritime Continent' (Indonesia and the North of Australia), the Congo River Basin, and the Amazon River Basin.
The forests of Amazonia play a critical role in regulating climate at both regional and global levels. The forests act to pump heat into the atmosphere, cooling the tropics and distributing heat to temperate zones. At the local level, deforestation may increase temperatures, decrease rainfall and disrupt hydrological cycles. Moreover, massive quantities of carbon are locked up in the forest biomass, which, if released, would add considerably to global warming.
To find out what happens over the undisturbed rainforest, a joint Anglo-Brazilian team of scientists conducted experiments which showed that 70 percent of the radiation from the sun goes into evaporating water, leaving just 30 percent to heat the air and general surroundings. They found that 17 percent of precipitation is intercepted by the canopy and evaporates before reaching the ground, while more than 30 percent of rainfall is drawn back into the atmosphere through plant transpiration. The remaining 50 percent runs off. The forest thus feeds the atmosphere which, in the turbulent conditions over the forest, forms cumulus clouds, and so the rain is returned again.
Enormous energies are involved in evapo-transpiration of water over the Amazon Basin - the lifting of 6.5 million million tonnes of water over the year is equivalent to the explosion of 5 million atomic bombs every day. Conversely, when rain precipitates from clouds, latent heat is released and becomes available for heating the atmosphere. Latent heat release through precipitation is more important as a factor in warming the air column than direct, sensible heat radiation from the sun, which is available to heat the air column by less than 2 degrees C per day.
The sun is the most important source of energy sustaining life. The bulk of solar energy reaching Earth's surface is spent in the evaporation of water (generating latent heat) and in heating the air (producing sensible heat). Research shows that, in Central Amazonia, about 80 percent of solar energy is used in evapotranspiration (evaporation plus plant transpiration), while the rest warms the air. Over upland forest which is never flooded, most of the water vapour in the air comes either from the transpiration of plants (60 percent) or from rainfall intercepted by the forest canopy and litter layer (40 percent). In Amazonia, half of the rainfall comes from local evaporation and the other half from the Atlantic Ocean. By comparison, in temperate latitudes, local evaporation constitutes about 10 percent of precipitation.
Climatologists have long recognised the importance of latent heat as a means by which solar energy received in the tropics can be distributed over the higher latitudes, thus evening out the surface temperature of the earth.
Moisture-laden air rising from the tropics is pulled towards the north-east in the northern hemisphere, and like a mirror image to the south-east in the southern hemisphere. The winds generated by this movement of air are known as the westerlies. They are counteracted, to their north and south respectively, according to hemisphere, by the easterly trade winds, which by their movement towards the tropics complete the circulation. The entire system of air currents from the equator up to higher latitudes and back again constitutes what has come to be called the Hadley Cell Circulation, after the eighteenth century scientist. Clearly, a change in the total quantities of water carried in this circulating system, as might result from deforestation of the tropics, will affect the transfer of heat from the equator polewards. It might also have some bearing on the expansion of deserts in the sub-tropics of both hemispheres.
Amazonia and the Chemical Composition of the Atmosphere.
Among earth's atmospheric gases are a group known as the greenhouse gases which allow solar energy to pass down through the atmosphere but absorb heat radiated from the earth's surface. The main absorbers of this infrared radiation are water vapour, carbon dioxide (CO2), ozone (O3), methane (CH4), nitrous oxide (N2O), and the chlorofluorocarbons (CFCs). While the role that tropical forests play in the carbon cycle is well known, and there can be no doubt that deforestation is contributing significantly to global warming, our understanding of the full contribution of tropical forests to the chemical composition of the atmosphere is limited.
Evidence suggests that man's agricultural activities over the past 150 years have contributed an amount of carbon dioxide to the atmosphere comparable to the total emissions for fossil fuel combustion. The accelerated deforestation of the tropical rainforest is having a marked effect on atmospheric CO2 levels.
Deforestation of Amazonia contributes to the enhancement of the greenhouse effect both by biomass burning and by destroying the trees which fix carbon through photosynthesis. The Amazon has a storage of biomass equivalent to 50 billion metric tonnes of carbon which, if burned, would release about 11 billion tonnes of carbon and would increase the concentration of CO2 in the atmosphere by 3 to 5 parts per million.
Local Climatic Effects.
Forested regions have a lower albedo (surface reflectivity) than regions with less vegetation, and therefore absorb more solar radiation and have more energy to be apportioned between latent and sensible heat. Deforestation modifies this division of energy with the result that the amount of energy available for heating the air increases, and the amount that goes into evapo-transpiration is reduced. This leads to an increase in the range of temperatures, with maximum temperatures increasing and minimum temperatures decreasing. Paradoxically, with the reduction in rainfall, water runoff may increase, with higher flood peaks. The main causes of increased runoff after deforestation are soil compaction (by animals and machines), which reduces infiltration, and the increased amount of rainfall that reaches the soil, in the absence of the forest canopy.
Moreover, when large areas are deforested, regeneration to the original state may take as long as 300 or even 1000 years, especially when heavy erosion has taken place.
If deforestation were to continue at exponential rates, the entire Brazilian Amazon would be deforested in less than 15 years. The climatic consequences alone make it imperative that sustainable forms of land use are found for the region which will allow the forest cover to remain intact.
Unsustainable Forestry in Finland.
Deforestation in the tropics may pose the greatest threat to climate stability, but unsustainable forestry at higher latitudes is contributing significantly to global warming. In Finland, the draining of vast areas of peatlands for forestry has resulted in huge increases in carbon dioxide emissions.
During the last few decades, one half of the 10.5 million hectares of peatland in Finland have been drained, mostly for tree plantations. Drained mires now cover more than a fifth of the country's land area, and it is predicted that by the year 2000 about 15 percent of Finland's wood production will come from drained mires. despite the adverse effects of this process on waterways and wildlife, environmentalists have so far (1991) been unsuccessful in trying to stop the draining of wetlands. Increased international concern about global warming may, however, change the situation.
Over thousands of years, a massive amount of carbon has gradually been accumulated in mires and swamps. In Finland, forests contain on average about 10 times, and peatlands about 100 times, more carbon than the atmosphere above them. The draining of mires may already be causing more annual carbon dioxide emissions in Finland than the national consumption of fossil fuels.
Global warming is expected to be most extreme near polar regions. This could dramatically accelerate the decomposition of peat in the drained mires.
Swamp soils tend to produce methane when waterlogged, but consume it when dry. As methane is a much stronger greenhouse gas than carbon dioxide, it has been argued that methane reduction would at least partly compensate for increases in carbon dioxide emissions. But it appears that only some types of mires produce methane, and the majority of mires drained in Finland have been the type unlikely to produce much methane.
Only if Finland's timber harvests are reduced will it be possible to reverse the destruction of peatlands, preserve the country's remaining wilderness areas and maintain or increase the carbon stored in its forests.