Global warming is not necessarily a problem for humanity. The contribution of deforestation in Amazonia to global warming is insignificant. The priority for humanity is modern development not conservation.

Deforestation and land degradation, pollution of marine and fresh waters and depletion of the ozone layer–these and other environmental issues have received widespread attention in the media. These problems somehow seem local and solvable. A landfill site can be monitored by a local authority and just stopping its use will significantly reduce the risk of pollutants entering the water supply. If necessary we have the technology to clean it up. Global warming is thought to be different. It is said to be a global manifestation of our pollution of the planet. It also grips us with the fear of the unknown–an insidious global danger. The solutions proposed range from dramatic changes in lifestyle to de-industrialisation and population control. Many fear that the action we take now might already be too little too late.
What are the facts? There is much anecdotal evidence that global warming is occurring– hurricanes in the Caribbean, the break-up of Antarctic ice shelves and warm summers in England. But what are the likely implications of warming and is the science of climate change now scarcely in dispute as is widely claimed? Global warming theory became scientific orthodoxy with the publication of the first report of the Intergovernmental Panel on Climate Change in 1990. The IPCC was set up in 1988 by the UN Environmental Programme and the World Meteorological Organization to assess the scientific evidence on climate change and its impact and to formulate a response. In its 1992 report the IPCC predicted a best estimate of a global mean temperature rise of 2.5°C in the next 100 years
and 0.5°C by 2010. Net emissions from changes in tropical land use have also been brought into the frame as responsible for 15 per cent of net anthropogenic emissions (Radiative Forcing of Climate Change, Report of the Scientific Assessment Working Group of the IPCC 1994).
Assuming this to be the case for the moment, does it matter? The most important point to appreciate from studies of past climates is that the earth’s climate is forever changing. We live in the period of time that geographers call the Holocene. This is the present warm period that has lasted for about 10,000 years. Prior to the Holocene was the Pleistocene which is synonymous with the alternation of ice ages, lasting about 100,000 years and short inter-glacials, lasting about 10,000 to 20,000 years. In fact most earth scientists regard the Holocene as an inter-glacial, with the onset of a new ice age not too far distant in time. The past temperature (palaeo-climate) record is preserved in the ice sheets of Greenland and Antarctica. In the last few years much effort has been directed at extracting continuous ice cores of 3-4 kilometres depth which hold high resolution palaeo-climate records of the last 100,000 to 250,000 years. These tell us that compared to the more distant past, we have had remarkably stable temperatures in the Holocene. Even in the Holocene temperature change is observed.
Change is the norm and nature has no preferred state. Should we have a preferred state from a human-centred perspective? Reconstruction of palaeo-climate and palaeo-environments shows that the ice-age earth was a truly dreadful place. As well as mean global temperatures more than 4°C colder than today, ice age climates were more arid, there was no Indian monsoon, vegetation survived in isolated refuges and there was higher atmospheric circulation. The Amazon forest was reduced to a small refuge and almost wiped out. By contrast, 6,000 to 7,000 years ago was what geographers term the mid-Holocene thermal optimum, when global mean temperatures were some two to three degrees centigrade warmer than present. With warmer climates comes increased precipitation and in the Holocene optimum global net precipitation was nine per cent higher. So, for instance, the Sahara desert, which was considerably more extensive during the Pleistocene ice ages, effectively did not exist. The Savannah which replaced it was hospitable to human life and it was only with the general cooling after the Holocene optimum that the Sahara grew to its present extent. There were some areas of increase aridity, such as Turkey and the Rockies but in general the Holocene optimum meant a more fertile and productive earth.
We have nothing to fear from nature with global warming. Some areas of productive farmland would be lost but they would be more than replaced by new areas for agriculture. A flourishing Sahara desert surely would be a good thing on a global scale. So just as ‘scare’ stories about Britain acquiring a Mediterranean climate can make us say ‘roll on global warming’, so does everything history has to tell us about the state of a warmer world. But what about local extremes of climate that the environmental disaster lobby predict? To look at this issue we first have to understand the causes of climate change.
The accepted theory of climate change shows that in palaeo-climates the carbon dioxide content of the atmosphere broadly responds to global temperature change. Note the chain of causality: historically, carbon dioxide concentrations have followed climate change, rather than forcing change. As important as this observation, is that even though this is true for the big picture on the scale of tens of thousands of years over small time intervals of a few thousand years, the temperature record and carbon dioxide record can be moving in opposite directions. This needs to be borne in mind when meteorologists are making their observations over periods of decades and at best hundreds of years (although without the global coverage of instrumentation).
So for scientists–the ‘sceptics’ - who reject the notion of anthropogenic induced global warming, there is plenty to get their teeth into. Certainly we should be sceptical of assertions that extreme weather events experienced today are linked to rising carbon dioxide levels. Assuming that increased concentrations of carbon dioxide can force warming, will a warmer or a warming world be more unstable even if it is overall perhaps more hospitable to human life?

Extreme global events
It is often argued that the very rate of global climate change is the problem and likely to cause extreme global events. Research into extreme geological events is certainly some of the most exciting research being undertaken at the present time: the idea that huge tsunami waves would have battered the eastern seaboard of America triggered by submarine slumping in the Canary Islands; the possibility of widespread volcanic dust in the western US and the implications for large-scale volcanism; and of course the realisation that a comet impact probably caused the extinction of the dinosaurs. The projected rise in global mean temperature itself might not be so alarming but extreme events could be. In this category of extreme events we have to include changes whose very speed is problematic rather than necessarily the magnitude of the change, which if slower could be accommodated.
Now the ‘rate of change’/extreme global events’ argument must be treated with some caution. To begin with, the global climate in the past has clearly changed far more than the projected changes of the Intergovernmental Panel on Climate Change. Secondly most climate models which look at the consequences of doubling carbon dioxide do just that. At year X they double carbon dioxide content of the atmosphere. It can hardly be surprising that if you suddenly change the inputs into a computer programme, you will get great lurches in the predictions made by the programme, which have no bearing on reality.
The ‘extreme events’ case has most recently been argued by the chief scientific adviser to the British Government, Sir Robert May FRS. One of the problems raised is the increased likelihood of tropical hurricanes in a warmer world. Models have been constructed which back up this idea. The general case for more violent atmospheric circulation globally is not borne out by the historical evidence, again from deep ice cores: these indicate more stability in a warmer world. The chief scientific adviser also raised the possibility that the Gulf Stream, responsible for bringing warmth to north-west Europe, could be shut off. This is of course scary stuff for while the world warms Britain would turn into a sub-Arctic wasteland. The argument for this is based on the idea that increased precipitation in the North Atlantic region and increased fresh water run-off, would reduce the salinity of surface water. Water will therefore be less dense and would not sink so readily. The geological records suggest the opposite happened– warmer climates meant stronger deep water formation. (The initiation of northern hemisphere glaciation, M E Raymo, Annual Review of Earth Planetary Science, 1994)

Contribution of deforestation to global warming
Tropical moist lowlands forests and especially the largest area still remaining, the Amazon rainforest, have become a particular focus of attention. Not just for the question of the loss of biodiversity but also for the impact of changes in land use on net greenhouse emissions. Satellite estimates of the rate of tropical land use change produced in the early eighties, (later found to be gross exaggerations), contributed to fears that were raised as the global warming debate was getting under way. Satellite measurements of average yearly deforestation were later revised down from 80,000 square kilometres to 20,000 square kilometres.