Climate Impact
Carbon dioxide is a trace gas that has a strong greenhouse impact on the Earth’s atmosphere, reducing the re-radiation of the Sun’s heat into space. The total mass of atmospheric carbon dioxide is approximately 3,000 gigatonnes or about 0.04% of the total atmosphere. But this proportion is presently increasing at a rate of around 0.41% pa exponentially.
The Earth is presently in a warming phase in its long term cycle between ice ages. The sun is also getting hotter in its cyclical temperature variation. During the past two centuries human population has exploded and mankind has become increasingly dependent on fossil fuels that release CO2. Warming in turn releases more CO2 into the atmosphere from natural sources, creating a potential feedback multiplier. With close monitoring over the past 50 years (and evidence from ice cores, sediments and so on) it is now clear that anthropogenic (human generated) CO2 is the greatest component in the observed increase; and thus a contributing factor in (rather than an outcome of) the global warming presently observed.
For the past 50 years petroleum has been the biggest fossil fuel source of anthropogenic CO2 but historically coal remains the major contributor and may again overtake petroleum, as oil resources are expected to be depleted first. Natural gas contributes about half as much CO2 as petroleum liquids and the calcination of lime (for cement) is a small but significant contributor.
The other great, and often overlooked, source of anthropogenic carbon dioxide is direct human impact on the environment’s natural storage and release mechanisms. The natural carbon cycle produces and absorbs an order of magnitude more CO2 than is released by fossil fuels annually. This natural cycle is being heavily disrupted by human population growth.
Over the past 100 years human population has grown by five billion people, from less than two billion in 1910 and less than a billion in 1810. We will pass seven billion in mid 2012.
The impact of this vastly increased human population through deforestation, broad acre agriculture, pastoral/grazing activities, excessive consumption of water, rubbish dumping, pollution of streams, rivers and oceans, over fishing and fire lighting is thought to exceed the release of CO2 for energy production.
In 1997 peat burning, in Indonesia alone, may have contributed as much as 10% of the total CO2 released that year. The pressures of overpopulation and land degradation in the third world combine with rapidly growing energy demands in the second; and too many over-consumers in the first; to make the present global warming trend a serious threat to the future of humanity.
Rapid global warming poses serious threats to economic crops and species habitat and is expected to result in increasingly rapid species extinctions. Higher atmospheric and oceanic energy levels will increase extreme weather events and change rainfall patterns. These outcomes are increasingly evident. The melting of the remaining land based ice and ocean expansion may inundate some economically important coastal areas and habitats.
Although sea level rise is presently the least evident outcome of recent warming it is the aspect most focussed on in public debates. Sea level rise appears to have been relatively continuous for the past 7000 years as land based ice has steadily contracted.
Since accurate satellite based observations began in 1993 sea level change has been quite linear averaging 3.4 mm per year. Satellite observations accord with older tide gauge data and together these suggest that globally mean sea level has risen by about a foot over the past 100 years, in line with the long term trend. This is difficult to confirm accurately as in many places the changes in land elevation, relative to mean sea level, are greater than sea level rise due to movements in the earth’s crust. In the Mediterranean/Aegean classical ports like Ephesus in Turkey are now six kilometres inland whereas others are under the sea.
The metre or more changes projected by glaciologists for the next 100 years are predicated on very much faster ice melting rates in Antarctica and Greenland due to accelerating warming; not on widely publicised melting of floating sea ice that has no significant impact on sea level (as pointed out by Archimedes). While these melting effects are not yet producing unusual sea level increases, all sea level rise, particularly that due to expansion as a result of warming, contributes to greater tidal surge, altered currents and more energetic cyclones.
The recent population explosion and the shortening time frame for significant variations in the coastline, from thousands to hundreds of years, could result in mass displacements and migratory (refugee) pressure, as the recent Garnaut Report warns:
If sea level rises by a metre or more this century and as much again in the first half of the next, and displaces from their homes the people of the low-lying coasts and river banks of the island of New Guinea, it will not be a problem for Papua New Guinea and Indonesia alone.
If sea level rises and displaces from their homes a substantial proportion of the people of Bangladesh and West Bengal, and many in the great cities of Dhaka, Kolkata, Shanghai, Guangzhou, Ningbo, Bangkok, Jakarta, Manila, Ho Chi Minh City, Karachi and Mumbai, it will not be a problem for Bangladesh, India, Pakistan, China, Thailand, Indonesia, the Philippines and Vietnam alone.
If changes in monsoon patterns and the flows of the great rivers from the Tibetan plateau disrupt agriculture among the immense concentrations of people that have grown around the reliability of water flows since the beginning of civilisation, it will not just be a problem for the people of India, Bangladesh, Pakistan, Vietnam, Myanmar and China…