Way back, long before 1750, the planet supported eight billion hectares of forest. These were vast, healthy carbon soaks and storehouses, rain makers, weather moderators and, of course, mega-rich biological systems. Since that time, humans have destroyed 6.3 billion hectares, leaving only 1.3 billion hectares of forest. Naturally (or unnaturally), this has vastly reduced the earth’s water cycles, weather patterns and ecological systems. But most importantly, this destruction has dramatically reduced the earth’s ‘lung capacity’.
The degradation of forests and the soils they grow in could easily account for the increase in carbon dioxide (CO2 ) levels after 1750. In the past, increases in CO2 have been absorbed in the atmosphere fairly readily (for instance, emissions from volcanic activity), as shown by the Vostock ice-core samples. This natural absorption of carbon is called biosequestration.
Clearing and logging the world’s forests has damaged its capacity to absorb CO2 . This forest-stripping habit of developing civilisations goes way back to pre-Christian times. Burning forest biomass for agriculture, building war ships and fuelling metal and glass furnaces not only put large whacks of carbon into the atmosphere but also took away the planet’s ability to absorb even more carbon. When forests ran out, the ‘civilised people’ began burning other carbon, the fossilised living matter, now known as fossil fuels (coal and oil).
We still pilfer and burn these ancient carbon stores to increase our comfort, expand industries and consequently increase our numbers, creating a momentum that will be hard to slow down let alone stop . Over thousands of years, we have built up a serious debt to the planet’s natural carbon stores.
To put it simply, we can’t pay back this debt simply by slowing down our burning of oil and coal by using alternate technologies and biofuels. We need to immediately start soaking up the CO2 that we’ve put into the air above us over the centuries and transform it back into solid carbon-storage vessels called forests and trees.
“A tall wet Eucalypt forest is one of the greatest carbon storage units on the planet. It can store 1,500 tonnes per hectare without cost or effort. Nothing else can do this.”
Climate chaos is unavoidable even if we stop all industry and transport globally. Due to the lag effect from last century’s high CO2 releases, during the coming decades we will be hit fully. If you do the sums, we should reach the critical 450 ppm of atmospheric CO2 very soon. (But don’t get depressed yet – read on a bit further.) This is a tipping point expected to start a rollercoaster ride of unstoppable carbon release. Melting tundra and ice-caps, changed ocean currents, forest fires and the other disasters in waiting would all release more megatonnes into the atmosphere. If you take into account methane and other greenhouse gases, we are already at 430 ppm. So no amount of wind turbines, nuclear plants, fancy light bulbs or bicycles will stop this latent load of carbon dioxide whacking the planet for a sixer.
But wait! We’re coming to the good news…
Forests – the lungs of our land
The earth and its reckless human passengers cannot avoid the CO2 levels of 450 ppm that will land us in the poo within a couple of decades. But if we start restoring forests like our lives depend on it, there is hope.
Since we started burning fossil fuels for everything from smelting iron to making jet fuel, it is estimated that we’ve sent some 300 billion tonnes of land-based carbon up in smoke. Compare this to the more than 2,000 billion tonnes that scientists calculate we have put into the sky by knocking down forests and degrading soils. Calculations suggest that the world’s original forests biosequestered carbon at about 300 billion tonnes a year.
If we replaced just 5% of the original biosequestration ability of the world’s forests (ie 15 billion tonnes of carbon a year) it should soak up the seven billion tonnes of carbon we currently burn up each year, with some to spare for absorbing our past emissions. This would go a long way towards calming the global climate chaos we are seeing. Practical and profitable options for doing this already exist.
Forests as heat moderators
The earth’s original heat balance also depended largely on forests and their cloud-making talents. To a large degree, clouds and rain are a result of the transpiration of water from forests. If clouds don’t form, less of the sun’s heat is reflected back, causing the ground to heat and less rain to fall. This forest – cloud – rain process can govern more than 50% of the earth’s heat balance. Temperature differences of 10^o C can show up between adjacent areas – one forested, one cleared – because of the cooling effect of clouds and rain. Past forest clearing could have played a large part in global water-dynamics, upsetting the earth’s heat balance and triggering regional and global warming. (The Mediterranean, Middle East and Central America used to have a healthy cover of forests.) Add to this the greenhouse effect of increased CO2 and we have some serious human-induced climate chaos.
Forests – the climate cure
Letting large areas of cleared land regrow into natural forests should give us a fast-acting remedy for restoring natural water and heat processes, while locking away loads of the carbon that’s causing problems overhead. But just slowing down our burning of carbon fuels might take decades, or even a century, to have an effect. That’s assuming the population doesn’t keep growing. If cloud densities were increased by 3% globally as a result of growing areas of forest, and solar radiation reflected back to space increased by about 1%, this should theoretically cool the planet and reduce CO2 levels back to pre-industrial levels.
The solution is so obvious. However, governments and even the Kyoto Protocol are not yet considering forests as the major tool for reducing climate chaos. There are still too many easy profits to be made through their destruction.
Jill – summarised from an article published in the April – May issue of Nature and Society and from a transcript of the ABC’s ‘Science Show’ 4.8.07.