IPCC Report: Humans are the ‘dominant cause’ of global warmingS

Our climate is changing, no doubt about it. The festering controversy we're in has been about whether humans have anything to do with it. A comprehensive report by a UN-sponsored climate panel may now finally put the issue to rest — and we're most certainly to blame.

Top image: Global Patterns of Carbon Dioxide. Credit: NASA Earth Observatory.

This is the fifth report produced by the UN’s Intergovernmental Panel on Climate Change (IPCC). The IPCC was launched by the United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO) in 1988 to “provide the world with a clear scientific view on the current state of knowledge in climate change and its potential environmental and socio-economic impacts.” The IPCC’s work is commissioned by 195 countries, which is basically everybody.

The new report — the first of three comprehensive studies to come out this year — makes one of the strongest claims yet in support of the hypothesis that human activity, namely the relentless pumping of greenhouse gases into the atmosphere, is what’s behind climate change — an effect climate scientists refer to as anthropogenic global warming.

"Unequivocal"

To reach this conclusion, IPCC scientists considered a host of factors, including changes to the ground, air, and oceans. They looked at anthropogenic cooling effects and the potential for natural causes. The scientists also considered geological data dating back for thousands of years.

According to the report, global warming is “unequivocal,” and since the 1950s it’s “extremely likely” that human activities have been the cause. The IPCC climate scientists are 95% confident that we’re behind global warming, but their best estimate is that is that we’ve caused 100% of global warming over the past 60 years. Over that time, scientists have observed changes to the environment that are “unprecedented over decades to millennia.”

Indeed, the report shows that concentrations of carbon dioxide and other greenhouse gases have increased to levels that are unparalleled over the past 800,000 years. Since the onset of the industrial revolution, the burning of fossil fuels has been the primary force behind the observed 40% increase in atmospheric carbon dioxide concentrations.

Netting Out External Factors

The scientists also considered the effects of aerosol, which has a cooling effect. From the report:

The observed warming since 1951 can be attributed to the different natural and anthropogenic drivers and their contributions can now be quantified. Greenhouse gases contributed a global mean surface warming likely to be in the range of 0.5°C to 1.3 °C over the period 1951−2010, with the contributions from other anthropogenic forcings, including the cooling effect of aerosols, likely to be in the range of −0.6°C to 0.1°C.

So what this means is that our planet has experienced 0.6°C average global surface warming over the past 60 years. Greenhouse gases can be attributed to about 0.9°C of this warming, but it has been partially offset by about 0.3°C cooling from human aerosol emissions.

Interestingly, the panel considered natural external factors, like solar activity and ocean cycles. But:

The contributions from natural forcings are likely to be in the range of −0.1°C to 0.1°C, and from internal variability likely to be in the range of −0.1°C to 0.1°C.

Meaning that natural factors have not had a measurable influence on global temperatures.

What We Can Expect

The panel predicts that global temperatures are likely to rise by 0.3 to 4.8°C (0.5-8.5°F) by the end of the century. But that depends on how we control carbon emissions from this point onwards, and whether or not we engage in geoengineering projects. And in fact, earlier this week the IPCC scientists said that the world won't’ cool without geoengineering. Indeed, the IPCC report went on to say that climate change will continue for many centuries even if carbon dioxide emissions are stopped.

As for sea levels, they will rise at a faster rate than what has been experienced during the past 40 years. By the end of this century we should expect to see the water rise anywhere from 26 cm to 82 cm (10-23 inches).

The IPCC scientists are also “virtually certain” that the upper ocean has warmed from 1971 to 2010. They say the ocean will continue to warm this century, with heat penetrating from the surface to the deep ocean.

Lastly, the report notes that we should expect to see Arctic sea ice continue to melt.

Worryingly, all of this challenges the two primary resources of humans and ecosystems, land and water.

"Our assessment of the science finds that the atmosphere and ocean have warmed, the amount of snow and ice has diminished, the global mean sea level has risen and that concentrations of greenhouse gases have increased," noted Qin Dahe, co-chair of an IPCC working group.

Countering the Skeptics

As many climate change deniers are apt to point out, there’s been a so-called pause in the increase in temperatures since 1998.

The IPCC report downplayed this observation, stating that 15 years is too short a period of time to draw any conclusions. The panelists partially ascribed the lull to El Nino effects. But they also stated that, "Likewise we have insufficient data to adequately assess the forcing over the last 10-15 years to establish a relationship between the causes of the warming."

Read the entire report here.