We cannot stop global warming and climate change, can we?

Reviewing the last IPCC AR4 report which finalized in 2007 and Copenhagen Diagnose which published in 2009 reveals that we most likely are incapable of stopping impacts of global warming and climate change despite all mitigation measures and sustainable development practices.

According to IPCC AR4, 2007: 

There is high agreement and much evidence that with current climate change mitigation policies and related sustainable development practices, global GHG emissions will continue to grow over the next few decades. Continued greenhouse gas emissions at or above current rates would cause further warming and induce many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century.

• Temperature will increase 2 to 4 °C
• Sea-level will rise 0.2 to 0.6 m
• More snow cover and ice loss
• Continuous change in wind and precipitation pattern
• More frequent extreme weather events (heat waves and heavy precipitation) 

Anthropogenic warming and sea level rise would continue for centuries due to the time scales associated with climate processes and feedbacks, even if greenhouse gas concentrations were to be stabilized.

According to Copenhagen Diagnose, 2009: 

Most recent climate change observations since close-off of material for the last IPCC report shows that:

Rapid Arctic sea-ice decline: Summer-time melting of Arctic sea-ice has accelerated far beyond the expectations of climate models. The area of summertime sea-ice melt during 2007-2009 was about 40% less than the average prediction from IPCC AR4 climate models.

Current sea-level rise underestimated: Satellites show recent global average sea-level rise (3.4 mm/yr over the past 15 years) to be ~80% above past IPCC predictions. This acceleration in sea-level rise is consistent with a doubling in contribution from melting of glaciers, ice caps, and the Greenland and West-Antarctic ice-sheets.

Sea-level predictions revised: By 2100, global sea-level is likely to rise at least twice as much as projected by Working Group 1 of the IPCC AR4; for unmitigated emissions it may well exceed 1 meter. The upper limit has been estimated as ~ 2 meters sea level rise by 2100. Sea level will continue to rise for centuries after global temperatures have been stabilized, and several meters of sea level rise must be expected over the next few centuries.

Delay in action risks irreversible damage: Several vulnerable elements in the climate system (e.g. continental ice-sheets, Amazon rainforest, West African monsoon and others) could be pushed towards abrupt or irreversible change if warming continues in a business-as-usual way throughout this century. The risk of transgressing critical thresholds (“tipping points”) increases strongly with ongoing climate change. Thus waiting for higher levels of scientific certainty could mean that some tipping points will be crossed before they are recognized.

The turning point must come soon: If global warming is to be limited to a maximum of 2 °C above pre-industrial values, global emissions need to peak between 2015 and 2020 and then decline rapidly. To stabilize climate, a decarbonized global society – with near-zero emissions of CO2 and other long-lived greenhouse gases – needs to be reached well within this century. More specifically, the average annual per-capita emissions will have to shrink to well under 1 metric ton CO2 by 2050. This is 80-95% below the per-capita emissions in developed nations in 2000.

In summary:

• Global mean air-temperature is projected to warm 2°C – 7°C above pre-industrial by 2100.
• The wide range is mainly due to uncertainty in future emissions.
• There is a very high probability of the warming exceeding 2°C unless global emissions peak and start to decline rapidly by 2020.
• Warming rates will accelerate if positive carbon feedbacks significantly diminish the efficiency of the land and ocean to absorb our CO2 emissions.
• Many indicators are currently tracking near or above the worst case projections from the IPCC AR4 set of model simulations.