Do we really need a new international agreement on climate?

President Obama in the State of the Union Address, Jan 2015.

Photo Credit: National Memo.

  “No challenge poses a greater threat to future generations than climate change,” argued Barack Obama in January 2015.

This recognition of climate change by the world’s second largest polluter , a nation who previously remained firmly outside the Kyoto Protocol and scuppered the UN’s Copenhagen climate-change conference in 2009 should give a slight glimmer of hope for the upcoming COP21. But why is climate change such a great challenge? What are the facts behind it?  Does it really merit a new international agreement on climate in Paris?

The global concentration of carbon dioxide in the atmosphere, measured in parts per million (ppm), is the primary indicator of recent climate change. The highly cited Hansen et al. (2008) paper investigated the target level of atmospheric CO₂ that humanity should aim for in order to preserve a planet similar to that on which life and civilization have developed and adapted. When the paper was written, these 'safe levels' required CO₂ to be reduced from 385ppm (parts per million) to at most 350ppm. However, the latest observations of atmospheric CO₂ for September 2015 show these levels to have risen to 396.86 (fig. 1). Even more alarmingly atmospheric CO₂ levels broke the 400ppm milestone in March this year sending a stark warning before COP21.

Figure 1: Monthly mean atmospheric carbon dioxide at
Mauna Loa Observatory, Hawaii.

The IPCC, the leading international body for the assessment of climate change reported in its Fifth Assessment (2013) that the Warming of the climate system is 'unequivocal', with many of the observed changes since the 1950's being unprecedented over decades to millennia highlighting how human influence on the climate system is clear. The full report is 1535 pages long and so some of the key findings from the summary are presented below.

• Anthropogenic greenhouse gas (GHG) emissions since the pre-industrial era have driven large increases in the atmospheric concentrations of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) (fig. 2).

Figure 2: Credit: IPCC (2014).

• About half of anthropogenic CO₂ emissions between 1750 and 2011 have occurred in the last 40 years (fig. 3)

  

  Figure 3: Credit: IPCC (2014).

• Globally averaged combined land and ocean surface temperature data show a warming of 0.85°C over the period 1880 to 2012 (fig. 4)

Figure 4: Credit: IPCC (2014).

• Ocean warming dominates the increase in energy stored in the climate system, accounting for more than 90% of the energy accumulated between 1971 and 2010. The upper 75m warmed by 0.11°C per decade between 1971-2010
• The ocean has absorbed about 30% of the emitted anthropogenic CO₂, causing ocean acidification; the pH of ocean surface water has decreased by 0.1, corresponding to a 26% increase in acidity.
• The average rate of ice loss from glaciers around the world, excluding glaciers on the periphery of the ice sheets, was very likely 226 [91 to 361] Gt yr−1 (gigatonnes) over the period 1971 to 2009, and very likely 275 [140 to 410] Gt yr−1 over the period 1993 to 2009.
• Over the period 1901 to 2010, global mean sea level rose by 0.19m [0.17 to 0.21] (fig. 5). The rate of sea level rise since the mid-19th century has been larger than the mean rate during the previous two millennia.

  

  Figure 4: Credit: IPCC (2014).

In addition a highly topical piece of research was published this year on the Planetary Boundaries Framework. Although arguably subjective and somewhat controversial the paper provides a useful framework for assessing and defining a safe operating space for humanity based on the biophysical processes that regulate the Earth system. The research suggests that four of the ES processes/features (climate change, bio-sphere integrity, biogeochemical flows, and land-system change) exceed the proposed planetary boundaries.

The planetary boundaries framework Steffan et al. (2015)

The recognition that human activities have had major environmental impacts on the climate system has led to considerable debate within the scientific community with a push for the Anthropocene (the period of time when humans have had major, global impacts on the earths systems) to be designated as a formal geological epoch, leaving the era of the Holocene (Mackay, 2015).  Much of the debate surrounds the Anthropocene's start date. Crutzen and Stoermer (2000) who originally proposed the epoch suggest its beginning at 1850 in line with the start of the industrial revolution. More recently Steffan et al. (2015) propose the beginning of the great acceleration (post 1950) as a start date arguing that only after this point is there is 'clear evidence for fundamental shifts in the state and functioning of the Earth System that are beyond the range of variability of the Holocene and driven by human activities', based upon socio-economic and earth system trends. However, Ruddiman (2013) suggests that pre-industrial temperature changes caused by humans could be more than double the anthropogenic warming caused by the industrial era, more than doubling the cumulative effects of humans on global temperature to date.

It has been widely reported that that a 'hiatus' in the upward trend of global surface temperatures occurred between 1998 and 2012. However, a recent paper in Science suggests that this hiatus never occurred. Global trends are higher than those reported by the IPCC, especially in recent decades, and that the central estimate for the rate of warming during the first 15 years of the 21st century is at least as great as the last half of the 20th century. It should come as no surprise then that 2014 was the hottest year on record  with Noaa reporting that global average temperatures over land and sea surface for the year were 0.69°C above the 20th-century average.  Again, July 2015 was the hottest month on the earth since records began.

So what do these changes mean for the global economy? A new study published in Nature argues that we have dramatically underestimated the damage that anthropogenic climate change will do the global economy. The paper investigated data from 160 countries between 1960-2010 and found that productivity peaks at an average local temperature of 13°C. If regional temperatures are cooler, then warming benefits the local economy, but past that peak temperature, warming reduces economic productivity. There was only weak evidence that global warming would not impact economic growth in wealthy countries, even though it has previously been assumed wealthier countries would have the resources to adapt to a changing climate. If future adaptation follows previous progress, unmitigated warming is expected to reshape the global economy by reducing average global incomes roughly 23% by 2100. Moreover poor counties will be preferentially harder hit reinforcing the reality that poorer countries which arguably contribute least to the problem are the most vulnerable to the consequences.

Another somewhat alarming discovery published in Nature climate change estimates the economic impact of carbon dioxide and methane being released from permafrost as it thaws resulting from rapid arctic warming. It found that by 2200, when these emissions are expected to peak, the costs could be 0.7% of global GDP. These findings are echoed by Mark Carney, the governor of the bank of England who last month warned that measures to avoid catastrophic climate change are essential to avoid financial crisis and falling living standards calling climate change the 'tragedy of the horizon' - imposing a cost on future generations that the current generation has no direct incentive to fix.

This blog has only begun to scratch the surface into the very real, alarming and critical threat of anthropogenic climate change that faces humanity. I believe the evidence is too great for international inaction to continue. I have broadly outlined the extent and scope of the problem and why the Paris talks in December really are Crunch time for a new legally binding agreement that will enable us to combat climate change effectively and boost the transition towards resilient, low-carbon societies and economies. Next time I will discuss what climate changes are projected for the future. A particular focus will be on the 2°C target and why it has been set as the goal for global climate policy (and the aim for COP21) following the Copenhagen talks in 2009.