Global Change and Health - Euan G. Nisbet

a Zimbabwean perspective on what we may expect

Foundation Professor of Geology, Royal Holloway, University of London

Global Change is normal. Ever since the formation of the planet 4,560,000,000 years ago the environment has been changing. Over time the Sun has brightened, the spin of the earth has slowed, and the air has changed.

Today the air is almost entirely a biological construction. The Nitrogen is captured by life as fixed N, then eventually released again as dinitrogen to the air, with a cycling time of many tens of millions of years; the Oxygen and Carbon Dioxide are obverse and reverse of the photosynthetic coin, with the air being the waste dump for excess oxidant; and the methane and trace gases are all biologically managed. The biological greenhouse gases naturally warm the planet by about 33^oC, from -18^oC which it should be to +15^oC which it is. Only the argon in not directly managed by biological processes, and even the argon is indirectly influenced by the biological maintenance of temperatures suitable for liquid dihydrogen monoxide, which by its role in plate tectonics helps manage the continental crust from which the argon is released.

The most important greenhouse gas, by a factor of 100, is water. But cloud and vapour are responses to warming by evaporation the controlling gases are carbon dioxide and methane. Throughout geological time the greenhouse warming has fluctuated, depending on biological controls and probably also influenced by a-biological events like massive eruptions (most recently in the Cretaceous, which eruptions supplied the carbon for much of the oil in our petrol).

The natural vegetation of Bristol at present is arguably tundra the high northern hemisphere is presently enjoying a brief break from a major glacial event. Or it was until humanity arrived. Had we not intervened, it is likely that the remarkably stable climate of the past 10,000 years would soon have ended: renewed glaciation is overdue. However, it is within our power easily to put off indefinitely the appointment with ice.

Humanity is adding to the air. When we arrived in Bristol the air had about 190 parts per million of carbon dioxide and roughly 0.75 parts per million of methane. When Burke was the MP the air had very roughly 250 ppm or slightly more of carbon dioxide. Today we breathe about 375 ppm CO₂ and 1.8 ppm methane: the Carbon dioxide has gone up by about half since before industrialisation and the methane has doubled. Methane is a much more powerful greenhouse gas (over a 20 year time period, it is 60 times as powerful weight for weight). Of the total actual human-caused warming increment today in 2003, about half is from added carbon dioxide, a quarter from added methane, and a quarter from added nitrous oxide and other gases.

The causes are varied. Carbon dioxide is added by combustion in industrial nations and deforestation and loss of soil carbon in the tropics; methane from gas pipe leaks, landfills, bovine eructation (but we have also eliminated bison and drained much wetland), and also from deliberate and wasteful tropical fires. Nitrous oxide is produced in fires and nylon manufacture.

Fourteen thousand years ago, the climate was glacial. Something happened we do not yet know exactly what it was. Within a very few years (inside a decade) the earths climate had reorganised and become much warmer. Around eleven to ten thousand years ago it cooled again, then a second very sudden warming took place, within one or two years. It took thousands of years for the ice to melt but the modern climate had set in.

The climate record is well preserved in ice cores in Antarctica and Greenland (and even Kilimanjaro, though that ice cap will be lost within this decade). It shows that these very sudden reorganisations of the climate system are regular events, every few tens of thousands of years. The Earths climate does not shift linearly, varying slowly as it is pushed by warming or coolling effects. Instead, it varies little, then very suddenly the winds and currents totally reorganise within a very few years. The climate has alternating stable states, with a zone between when either state is permissible.

The fear now is not that we may drop back to glaciation (though paradoxically that is possible if meltwater makes the north Atlantic too fresh and thus less dense): instead, the fear is that there is a new stable state up-temperature, which would suddenly appear. In such a transition of state the changes would be immense: it might cease to rain in large parts of India or Amazonia, or begin pouring in central Australia.

Climate change is exactly that change. Humanity is adaptable, and can cope with change, provided it is slow enough. Nature is adaptable and has always coped with change. But how slow is slow enough? very slow change will have little impact on Nature, except slowly to shift vegetation belts. In contrast, really fast change could, in principle, reduce the biosphere to microbes. Human beings are constrained by need for water and food, by borders, and by disease, in addition to economic factors. The richer humans are the more adaptable simply because they have the greater reserves more skill, more machines, bigger stockpiles. Poorer humans have slender reserves. When change occurs and the reserves are exhausted poor people become hungry, get sick, or move.

The most obvious change that will come in the next 20-50 years is in seasonal weather patterns frequency of droughts or floods, major storms. Change will come it is difficult and perhaps even irresponsible to forecast precisely where and how climate will change, but it WILL come. Many of these events do not kill directly they kill indirectly by disease epidemic (often from water), or simply by normal vectors of disease acting on weak hungry people.

Most communities are adapted to weather as it was thus wet areas expect water flows, dry areas expect drought. Epidemics come when the situation changes. Floods are obvious challenges sewage systems break down and drinking water is contaminated. In droughts there may not be enough water to move sewage (as happened in Zimbabwe last year). The larger impacts are of course via malnutrition both droughts and floods destroy crops. But usually people do not die directly from hunger they die when weakened in famines, but from diseases such as cholera in camps, or simple diarrhoea, or TB. Climate change, by stressing poor societies, creates a vicious circle famine drives people out of their home communities, then weak people congregate where all the other problems arise. Rich nations are lucky they have enough reserve of provision that even in extreme circumstances people do not die. The post-war famine in Europe was extreme so bad that Britain brought in bread rationing in order to feed Germany. The food shortage was very great - Germany was formerly dependent on its eastern farmlands - yet Field-Marshal Montgomerys administration managed to bring everyone through, without mass deaths. Why? skill, fairness, and good sewers, all lacking in many poor nations with far less food stress.

Pests and pest-borne disease are another expectation of climate change. But here too some perspective is needed. Ottawa was famous for its malaria; so was Cambridge (ague). When housing got better and windows were common, the transmission factor dropped below 1 and the disease died out. Today Florida is wet, warm, filled with mosquitoes, repeatedly visited by malarial people from South America, and has screen doors and hospitals. Malaria hasnt a hope in the UK: too many closed windows, and too many GPs.

But some diseases escape despite this Dengue, West Nile, Chikungunya, and Venezuelan

equine fevers may reach the UK.

In general, unless there is very vigorous and immediate action to isolate the infection,

many tropical diseases may become established.

Insects may threaten human health more seriously by indirect attack many infestations explode after by small changes. For example, in the 1980s, cutting forest in Mexico removed winter habitat for the Tennessee warbler. Then in summer in Canada there were less birds and the spruce budworm flourished: more worms meant that the birds were fully fed and the rest of the worms reproduced freely; the result was the elimination of huge areas of Canadian spruce forest. Two lessons come from this example: that the natural system has teleconnections; and that insects are non-linear. The bible has many accounts of the locust years. Global change will bring many locust years, and their health consequences.

The link between water-borne disease and famine has already been mentioned: in drought or flood, clean water is hard to come by, especially when displaced people congregate in huge numbers. The solution is good engineering, rather than emergency symptom treatment by doctors. Other than dealing with major epidemics such as AIDS, supplying clean water may well be the largest health challenge most moderately well-governed poor nations will have to face in the next 20 years. For the decent, not-too-corrupt president of a South Asian or African nation, faced with dry reservoirs or dams broken in floods as a result of climate change, the task may seem impossible. Then people will see their children die of diarrhoea. This is not dramatic: just quiet one-by-one family tragedy, but causes immense human misery. Here already is the impact of climate change.

Catastrophic change is something more obvious. The biggest catastrophe is a major reorganisation of the global climate system. The circulation of the air will change the jet streams will move. This took place twice in the recent past, very roughly about 14 thousand and 10 thousand years ago (12,000 and 10,000 BC). Both times the change was very sudden, within a few years. One year the world was in a glaciation; a decade later it was well into interglacial conditions. It took millennia for the ice to melt but on each occasion the climate was changed, permanently (at least for a few thousand years around 11 thousand years ago it slipped back to glacial before the flip back 10 thousand years ago).

A catastrophe like this would have immense human consequences. It would rain in future where it is drought now, and become dry where now it rains. For example, if the monsoon weakened, how would we feed India. Humanity would have to migrate en masse, and the medical consequences would be immense and unpredictable.

On a much smaller but still worrying scale, warming sea water can set off immense submarine slumps and landslips. The Storegga slide, off the coast of Norway, covered an area of sea bottom larger than Scotland with debris and put a tsunami wave over Inverness. Many hundreds of these slumps occurred roughly 15-8,000 years ago, and there are many that may be ready to fail in future. It is possible that the Lisbon Earthquake of 1755 was linked to a major slump that failed on warming seafloor sediment tens of thousands died. In recent years, lethal slumps occurred off New Guinea, Hawaii, Nice, Newfoundland, etc.

Major off-shore slips and slumps are low-probability nightmares very unlikely, but nevertheless the large failures can be very devastating. The medical consequences will overwhelm the local community the best planning is probably to accept this and try to be ready to come in quickly to help.

This may be the UKs most serious immediate danger of disaster for northern Scotland about comparable to the earthquake risk in New Zealand.

A warmer world is a world with more energy in the climate. Storms and major meteorological events are likely. In El Nino years, hurricanes are very rare in the Caribbean/NW Atlantic, but heavy rain and ice storms occur in winter in N. America; droughts occur in Africa, Australia, and eastern Latin America; conversely, in La Nina years hurricanes are common in the Atlantic. For the UK, many expiring Caribbean hurricanes turn into autumn storms, especially across Scotland before passing up to the Arctic and losing energy. Extreme storm events are probably more likely medically this will mean more injuries in winter in the UK.

It is likely that tornadoes will become more common this side of the Atlantic indeed, this may become the most obvious immediate result of warming, especially in Europe but also in the central to eastern UK.

For Africa and the tropical Americas, the impact will be greater catastrophic flooding that sweeps crops away. The worst storms are the Asian typhoons but Asia on the whole is better adapted to great storms.

We have several obvious tasks:

First, to attempt to moderate climate change. We cannot stop it. The CO₂ economy is so

important that no democracy will tolerate anything but a slow and phased reduction in emission. This cannot have any real effect on climate until about 2250 or later, as CO₂ has a lifetime in the air of several centuries.

However the second anthropogenic greenhouse gas is methane, with today in 2003 about half

the greenhouse impact of anthropogenic CO₂. In contrast, CH₄ has a lifetime of about 10 years. Vigorous action tomorrow to reduce methane emissions will have results by 2020.

The most obvious initial response would thus be to reduce methane emissions cutting landfill output, leaks from gas pipes, boilers, and gas wells, and reducing tropical wildfires in savanna grasslands and forests.

Secondly, there is a need to take preemptive action. Most important is probably to increase the reserves of the poor nations skill mostly, but also physical improvements, especially the provision of water and electricity for rural people.

Within the UK, the most likely needs will be:

a) provision for medical consequences of local catastrophe storm, tornado, flood, and in coastal areas, a very small but real risk of tsunami.

b) expectation of tropical diseases. Most probably they will not take hold in the UK, but only if there is very vigorous and early intervention to track down the carriers.

c) looking after many people taking refuge from tropical disaster this, plus the diseases they bring, will be the chief medical consequence for the UK. Already the lethal combination of misgovernment and drought in Zimbabwe is perhaps one of the UKs major sources of new AIDS and TB cases, a problem exacerbated in Africa by the UKs massive deliberate recruitment of medical skill from Africa.