Published every six years, the IPCC Assessment Reports are the most comprehensive international assessments on the state of climate science. Similar to prior studies, AR5 is the product of a consensus based process combining the most current scientific data with input from more than 800 climate scientists from dozens of countries.
The AR5 alerts on these key messages:
- Humans are largely responsible for rising global temperatures: global surface air temperatures have risen more slowly in recent years, but warming in the oceans has continued apace. In fact, the IPCC finds that our oceans retained more than 90 percent of the heat trapped by greenhouse gases since 1970. Rapidly warming oceans contributing to accelerates sea-level rise. In addition this, rising carbon dioxide emissions is making oceans much more acidic, which kills coral reefs, which support the livelihood of about 500 million people around the world.
- Many observed impacts are happening more quickly than previously predicted: the IPCC finds that Greenland and Antarctic ice sheets have melted several times faster over the past decade than during the 1990s. Overall, the extent of summer Arctic sea ice has shrunk more than 11 percent per decade. In fact, under higher future emissions scenarios, the IPCC finds that the Arctic could have ice-free summers by 2050.
- Climate change is creating more frequent and more intense extreme weather events: The IPCC finds that global warming is amplifying extreme weather and climate events regionally. This includes more frequent heat waves and a greater number of heavy precipitation events. In the North Atlantic, there has been a clear increase in the occurrence of intense tropical cyclones. Regional trends in drought and flooding are also emerging, with worsening conditions projected through the end of the century.
- Business-as-usual will lead us far beyond 2 degrees Celsius of warming: continuing business-as-usual emissions could mean the very worst case IPCC scenario, where global temperatures rise by more than 4 degrees Celsius above pre-industrial levels by 2100. This is the maximum level of warming that the international community agreed to under the United National Framework Convention on Climate Change (UNFCC).
- Cutting carbon dioxide (CO2) emissions is the most urgent imperative for global climate action: atmospheric concentrations of CO2 reached 400 parts-per-million (ppm) earlier 2013 –more than 25 percent higher than any time on Earth in the last 1 million years. The IPCC finds that to avoid more than 2 degrees of warming, global emissions must fall by an average of 50 percent below 1990 levels by 2050. This requires urgent action, as our energy systems will take decades to fully decarbonize, given the time it takes for power plants and vehicle fleets to turnover.
That’s the bad news, but solutions are available. Now is the time to act !!!.
Climate Change 2013: The Physical Science Basis. IPCC Working Group, contribution to AR5, September 2013