Disruption of the climate machine

The greenhouse effect is necessary for life on Earth. But when mankind disturbs this system, the climate machine gets carried away...

The greenhouse effect is shifting

The greenhouse effect is the property of our atmosphere that allows it to capture a portion of the infrared radiation emitted by the Earth. Thanks to this greenhouse effect, the earth's temperature is conducive to life. Some greenhouse gases (GHGs) occur naturally in the atmosphere: water vapour, carbon dioxide (CO₂), ozone, methane and nitrous oxide. Through its various activities (industry, agriculture, transport...), mankind emits these same gases into the atmosphere, which are in addition to those that are purely "artificial": halocarbons (gases derived from oil). Due to the increased concentration of atmospheric GHGs, the greenhouse effect increases. Ever since the beginning of the industrial era, this has led to "radiative forcing" representing 1% of the radiation received: the situation on Earth is evolving as if the sun had increased its power by approximately 1% ⁽¹⁾. This additional greenhouse effect is mainly due to CO₂ (55%), methane (15%), halocarbons (10%), ozone (10%), and nitrous oxide (5%) ⁽²⁾.

The analogy with a mountain lake, put forth by Jean-Marc Jancovici ⁽¹⁾, allows one to quickly understand the consequences of a shift of the greenhouse effect. When everything is in balance, a lake receives as much water from upstream as it supplies downstream, and its level is constant. If the melting snow increases the inflowing water, the lake level rises until the outflow rate increases sufficiently. Similarly, if children build a dam at the lake's water outlet, the lake level will rise until the water rises above the dam and the stream output rate returns to its original level. The same applies to our atmosphere: without human intervention, the outgoing energy flow (infrared radiation) compensates for the inflow (solar energy), and the Earth's temperature remains stable. By increasing the greenhouse effect, we limit the infrared radiation directed towards space. We are therefore building a dam where the temperature behind it is rising.

Other factors of change

The increased greenhouse effect is the main contribution of mankind's activities on climate change. However, other interventions affect the exchange of energy between Earth and space ⁽²⁾. The radiative forcing due to our use of land is mainly negative (it offsets the greenhouse effect): bare ground reflects more sunlight than ground covered with vegetation. However, melting ice or its covering with soot reduces this reflection. Aerosols also have a strong effect on climate: their fine particles have a direct effect, through their reflection of sunlight, and an indirect effect, through their influence on cloud formation. The overall impact is harmful to the greenhouse effect: it is commonly referred to as "global dimming" ⁽³⁾. It worries many scientists: in addition to its current impact, its upcoming decline (environmental standards are opposed to aerosols) could increase global warming.

The consequences of climate change

Climate change is a reality. The evolution of the Earth's temperature is one of its consequences: it has increased by approximately 0.7° C between 1906 and 2005. More worrying: even if mankind behaves in an exemplary manner with regards to the environment, global warming will climb to at least 2° C because of the inertia of the systems that are involved ⁽²⁾. The indirect consequences are numerous.

Global warming disrupts the water cycle. The melting of glaciers threatens the water supply of many countries. Moreover, it also causes a rise in the sea level: 3 mm. per year since 1993, representing between 20 to 60 cm. by 2100, and probably 2 metres by 2300 ⁽²⁾. Worrying figures when one considers that a one metre rise would require 150 million people to move ⁽⁴⁾.

Global warming threatens the entire living world. The changes in life cycles and in the allocation of space are already of concern to 50% of all species ⁽⁵⁾. A 2 to 3° C increase in temperatures would increase the risk of extinction of 25% of all species ⁽²⁾. However, it's the speed of change that could be fatal: only 50% of all species would be able to adapt to a 0.1° C change in temperature each decade ⁽⁵⁾.

Warming affects local climatic events. Between 1900 and 2005, rainfall has significantly increased in eastern North America, in northern Europe and in some parts of Asia, while decreasing in several regions of Africa (Sahel...), the Mediterranean and South Asia ⁽⁴⁾. In addition, IPCC ⁽²⁾ models predict an increase in the frequency of heat waves, periods of heavy rain, as well as the intensity of certain natural disasters (hurricanes...). These forecasts have already been observed by many of our planet's residents.

Faced with this climate change, adaptation strategies are needed. The revision of water supply channels; the evolution of private ski resorts' economic activities; the adaptation of agriculture; the anticipation of rising waters; protection against natural disasters... The cost of such adaptive measures is estimated at several tens of billions of euros per year for the entire planet, and it increases if we delay such investments ⁽⁴⁾. In addition, our infrastructures generally have a long life (between 30 and 100 years). Lastly, everything will probably require that we act quickly.

The voice of "climate sceptics"

History has led us to become suspicious of a singular mode of thinking. As a result, given the strong consensus within the scientific community, some have raised their voices to propose alternative interpretations of the current climatic situation. Although they are sometimes suspected of opportunism or of having links with the oil lobby, these theories fuel the debate on climate. Nevertheless, they should not detract from the environmental emergency that extends beyond the climate: even if you have doubts regarding climatic change, there is no denying the erosion of biodiversity; and while the extinction of species may not seem alarming, no one can ignore the upcoming shortage of raw materials. In short, no theory can justify inaction.

Written by Florent Planas for "One year for the Planet" (translated by Anyword).

Find out more…

1. Jean-Marc Jancovici, www.manicore.com
2. Intergovernmental Panel on Climate Change (IPCC), 4^th assessment report (2007)
3. L. Rotstayn et U. Lohman, Tropical rainfall trends and the indirect aerosol effect, (Journal of Climate, 2002)
4. Raphaël Trotignon, Comprendre le réchauffement climatique (Pearson, 2009)
5. Yves Sciama, Petit atlas des espèces menacées (Larousse, 2008)