The business community may be panicking over the IPCC’s suggested targets but if only they knew the cost of what we really need to do to combat global warming. Many commentators and policy makers fail to take into account the fact that the IPCC-AR4 2007 hardly takes carbon feedbacks into account, qualifying its CO2 projections in the following terms:
The emission reductions to meet a particular stabilization level reported in the mitigation studies assessed here might be underestimated due to missing carbon cycle feed-backs (see also Topic 2.3) AR4 caption to Table 5.1.
Yet despite the huge gap between the IPCC’s final report and the true scale of the challenge we really face once carbon cycle feedbacks are taken into account, IPCC projections form part of the basis for official CO2 emission-reduction policies.
These include the Kyoto protocol targets (at least 5% below 1990 levels in the commitment period 2008 to 2012), EU emission targets (20% of 2000 emissions by 2020) and the Garnaut Review recommendations (10% of 2000 levels by 2020 aimed at atmospheric stabilization at 550 ppm).
A principal question is whether stabilization of the climate can be achieved through limited cuts in the level of carbon emission, or whether further measures are required. The carbon emission trajectories appear to assume decade-scale to century-scale stabilization of committed atmospheric CO2 levels (Figure 1).
For example, a carbon emission ceiling at 25 Gigaton CO2 per-year (GtCO2/yr) in 2020, followed by emission reduction, is expected to lead to stabilization at CO2 levels at 445-490 ppm; A ceiling at about 40 GtCO2/yr in 2040, followed by emission reduction, is expected to lead to CO2 stabilization at 590-710 ppm.
But the concept of “atmospheric CO2 stabilization” is not borne out by evidence based on ice core studies of the behavior of the atmosphere during the last 640 thousand years:
(A) The long CO2 atmospheric residence time, on the order of centuries (15-30% is expected to remain in the atmosphere after 200 years), results in cumulative build-up of greenhouse gases. Given the Earth’s vast coal and oil shale reserves, continuing fossil fuel emissions at any level will therefore contribute to higher atmospheric CO2 levels.
(B) Carbon gas (CO2, CH4, CH4 hydrates breakdown) feedback effects from warming oceans, thawing bogs and drying vegetation (“No plant CO2 relief in a warming world“) and fires, not taken into account in the IPCC AR4 Report, enhance atmospheric greenhouse gases and temperatures.
The last factor is of key significance. Solar-triggered terminations of the ice ages display rising CO2 levels lagging behind temperature rise, indicating a dominant role of ice sheet melt/warming water feedback effects (Hansen et al., 2008), culminating in abrupt atmospheric events.
Greenland and Antarctica ice cores display climate tipping points on time scales of decades and even years (Steffensen et al., 2008. Science Express, 19.6.2008, DOI: 10.1126/science.1157707; Kobashi et al.,2008. Earth Planet. Sci. Lett. 268, 397; DOI:10.1016/j.epsl.2008.01.032).
Anthropogenic climate change since the mid 18th century works in reverse, where human-released greenhouse gases triggers melting of the polar ice sheets.
Earth atmosphere is fast tracking toward atmospheric conditions which existed in the mid-Pliocene about 3 million years ago, when CO2 levels rose to about 400 ppm, temperatures rose by 2 -3 degrees C and sea level rose by 25+/-12 metres.
Global investment in effective climate change mitigation and adaptation — solar-thermal, photovoltaic, hydrogen, wind, geothermal, dry rocks, soil carbon re-fertilization, forest planting, geo-engineering — on the scale of hundreds of billion dollars to trillions is required.
It defies contemplation that policy makers, willing to spend this kind of money to rescue failed vested economic interests from meltdown, have to date declined to attempt to mitigate the meltdown of the polar ice sheets.