The IPCC's 'Summary for Policymakers' A Comment

Recent reports from the Intergovernmental Panel on Climate Change's "Summary for Policymakers" make for alarming reading about the global warming phenomenon. How bad climate impacts will be beyond the mid-century depends crucially on the world urgently shifting to a development trajectory that is clean, sustainable, and equitable, a notion of equity that includes space for the poor, for future generations and other species.

Nagraj Adve (nagraj.adve@gmail.com) works and writes on issues related to global warming.

Every few months or so, I come across some fact when reading climate literature that just makes my stomach clench. This happened twice when reading the recently released Intergovernmental Panel on Climate Change’s (IPCC) “Summary for Policymakers” (henceforth SPM, or Summary). Snow cover in the Northern Hemisphere in June, says the SPM, has reduced by 11.7% per decade since 1967. Which means that snow cover in that month over the Northern Hemisphere has fallen to half of what it was less than 50 years ago. The second time was when reading that permafrost – frozen soil that extends several million square kilometres along the high Northern latitudes, frozen to several feet deep below the surface since the last glacial period, until now – has warmed by a staggering 3 degree Celsius (°C) in northern Alaska since the early 1980s and 2 °C in the Russian European north since 1971.
The IPCC, for those who, like me, came in late, every six years or so publishes assessment reports in three huge volumes on the science, impacts and mitigation respectively of climate change. The last such Assessment Report, the fourth, was in 2007. The document that has been just released worldwide is the SPM of the first volume of the Fifth Report, of earlier established climate science and of key peer-reviewed publications since 2007. The Summary is vetted by political elites of various countries before it is released, and has consequently often been criticised for being too conservative in some areas. Notwithstanding the truth of that, I must say that the IPCC assessment reports are extraordinary volumes. It is a pity that such compilations with the latest advancements in research worldwide are not also possible in economics, sociology, political science or whatever is the field of one’s interest.
The earth’s surface over each of the last three decades, says the latest Summary, has been warmer than any preceding decade since 1850, and has warmed by 0.85 °C since 1880 (the earth’s average temperature in 2011 was 14.47 °C). An average rise of 0.85 °C may not seem like much until we realise that barely 5-6 °C separate current temperatures from the peak of the last glacial period 20,000 years ago; that some regions, like the Arctic and the Himalayas, are warming much faster than this average; and that a number of species have already been rendered extinct by warming thus far. This temperature rise is also significant because it reversed a long-term downward trend in the earth’s average temperature, a natural decline that began roughly 5,500 years ago until about 1850 (Marcott et al 2013).
Between 1901 and 2010, says the Summary, sea levels rose by 19 cms on average worldwide. In recent years, this rise has increased to 3.2 mm a year. Much of this rise in the 20th century has happened because of ocean waters expanding as they get warmer, and due to glaciers melting. The third highest contributor to sea level rise, interestingly, is “land water storage” (p 7), groundwater and water from reservoirs that is being frenetically pumped and eventually finds its way to the sea. Water vapour levels have risen by 3.5% over the past 40 years, in keeping with the 0.5 °C warming in that time.¹ It is also “very likely” (90%-100% probability) that human influence has contributed to global-scale changes in the frequency and intensity of daily temperature extremes, and doubled the probability of heat waves occurring in some locations (p 13).
What, according to the SPM, is causing all this and more? Of the total greenhouse gases (GHGs) emissions since industrialisation began in the mid-18th century, 44% or little less than half has accumulated in the atmosphere, the rest being almost equally taken up by the oceans (making them more acidic), and by land-based ecosystems. As a consequence, the atmospheric concentrations of the three main GHGs, carbon dioxide (CO₂), methane (CH4) and nitrous oxide (N₂O), have risen to levels “unprecedented in at least the last 8,00,000 years”. They have risen to 391 parts per million (ppm), 1,803 parts per billion (ppb), and 324 ppb in 2011, respectively, a rise 40, 150 and 20% above pre-industrial levels. Carbon dioxide emissions alone from fossil fuels and cement production was nearly 35 billion tonnes in 2011, 54% above 1990 levels, the benchmark year against which GHG emission cuts are measured under the Kyoto Protocol, a benchmark some countries, like the United States, are trying to unilaterally shift to 2005.
More ‘Warming in the Pipeline’
The section on the energy imbalance caused by the main drivers of climate change, known as their radiative forcing,² throws up a number of interesting points about the present. One, there has been a huge jump in human-caused radiative forcing since the last Assessment Report in 2007, because of rising emissions and new measurements of the warming effects of black carbon (Figure 5: 31). Two, there has been a particularly sharp rise in methane’s forcing, a potentially sensitive issue given its connections with rice submergence farming carried out so widely in India and China. Whereas it is true that methane emissions have been rising since 2005 – no one has established why – in contrast to their plateauing since 1993, and that methane is 57 times as potent a gas as CO₂,³ the sharp rise in the latest report is partly because the calculation includes its indirect effects on stratospheric water vapour and ozone. Three, changes in the Sun’s solar irradiance clearly has no effect on global warming, measuring just 0.05 watts/m^2 since 1750, insignificant in comparison to human-caused forcing such as, say, carbon dioxide emissions (1.82 watts/m^2) and methane (0.97 watts/m^2). But the most significant thing about this section is about the future: it is particularly alarming that the radiative forcing from the three main GHGs mentioned above and from halocarbons are in the range of 3 watts/m^2, because there is a commensurate relationship between radiative forcing and eventual temperature rise, of roughly 0.75 °C of warming for every watt of forcing. The Summary does not say so, but this would imply that we are already committed to a warming above pre-industrial levels of about 2.25 °C, above the widely-accepted benchmark of 2 °C. Basically, the unavoidable “warming in the pipeline” will be a lot more than the 0.6 °C that is commonly accepted.
Besides giving a gist of present and past, the Summary also makes projections about future changes in the climate system, in the near-term (2016-35) and mainly for the end of the 21st century (2081-2100) relative to the period 1986-2005. It uses four possible pathways – representative concentration pathways (RCPs) 2.6, 4.5, 6.0 and 8.5 – each corresponding roughly to a level of CO₂ and other gases in the atmosphere by 2100 and a volume of CO₂ emissions until then.⁴ Basically, each pathway reflects possible energy choices and development trajectories.
For the near-term, temperatures will rise in 2016-35 by a further 0.3-0.7 °C relative to 1986-2005, a period that was already 0.6 °C warmer than pre-industrial temperatures. We in India should be concerned that increases in seasonal and annual mean temperatures are expected to be larger in the tropics and subtropics than in the mid-latitudes, relative to internal variability (p 15). The tropics are home to a huge number of the world’s known species, and which have historically evolved and been used to a relatively narrow temperature band. A small rise may mean that many tropical species have to migrate or become extinct. For instance, mackerel (bangda, aila) and oil sardines have already been moving northwards along both coasts of India as the ocean waters get warmer.
In the longer term, it is seriously alarming that much of north, west and central India would be 4-5 °C warmer by 2081-2100 if we stick to business as usual strategies (Figure 8: 34). Regarding the water cycle, it says that monsoon retreat dates will likely be delayed in many regions. Regardless of whether or not it was due to climate change, we have already seen the damage to crops that a delayed monsoon retreat this year caused in many parts of India. Finally, a nearly ice-free Arctic in September (the month of the lowest ice extent annually) before mid-century is likely for the trajectory RCP 8.5.
New Aspects in the Summary
Methodological innovations aside, this Summary has a number of new aspects. It says that sustained warming “would lead to the near-complete loss of the Greenland ice sheet”. That threshold is put at greater than 1 °C above pre-industrial temperatures (we are currently at 0.9 °C above) but less than 4 °C (pp 20-21). This is hugely different from the earlier Assessment Report 2007 which merely said that the Greenland ice sheet would lose mass with a warming of 1.9-4.6 °C. On the renowned website Real Climate (27 September), the scientist Stefan Rahmstorf pointed out that this 1.9 °C figure was one of the reasons why international climate policy set 2 °C as the benchmark for dangerous warming. What do these lower temperature figures for Greenland then imply for what is considered safe?
Two, with respect to droughts, the new report says that the earlier conclusions regarding increasing trends in droughts globally since the 1970s are no longer supported by more recent research. Having said that, regional droughts have increased in frequency and intensity, such as in the Mediterranean and west Africa.
Three, the increased loss of ice mass from the ice sheets in Antarctica and Greenland are staggering. The average rate of ice loss from Greenland has increased from 34 billion tonnes a year over 1992-2001 to 215 billion tonnes a year over 2002-11, over six times as much! Antarctica ice loss over these same periods has increased from 30 billion tonnes to 147 billion tonnes a year, nearly five times as much. These huge rises make them qualitatively different from any earlier IPCC assessment report.
Four Issues Worth Discussing
The latest Summary for Policymakers throws up a number of issues worth discussing. I will touch upon just four.
First, the supposed slowdown, or hiatus in global warming in recent years, much discussed in leaks and newspaper editorials before the Summary was released. The Summary itself says that the slowdown in surface warming since 1998 is due to natural variability and reducing forcing due to volcanic eruptions (which throw up particulate matter that tends to cool). Satellite data tells us that the earth’s energy imbalance due to GHGs has continued unabated in recent years. So if warming is not showing up in surface temperature data, we need to look elsewhere. Over 90% of the excess energy trapped by GHGs has been going into the oceans; the heat being trapped in the upper oceans alone (the top 700 metres) each year is over 40 times as much as the total annual energy consumption in the United States! But what has been exceptional in recent years is the warming of ocean waters below 700 metres. This has been happening, a recent paper (Balmaseda et al 2013) suggests, after 1998, precisely the period for which the slowdown in surface warming is reported. Much of this will show up as warming sooner or later.
Two, is CO₂ less potent than we earlier thought? The SPM has reduced the lower limit of the potential change in global mean surface temperature due to a doubling of CO₂ to 1.5 °C from 2 °C in the earlier assessment report. The scientist Michael Mann wrote (The Guardian, 28 September) that this lowered estimate is “based on one narrow line of evidence”, the recent slowing in surface warming, which, as discussed above, is more complex than it seems. What is more, this IPCC estimation of carbon dioxide’s potency is methodologically incomplete and hence an underestimate – it does not include slow feedbacks such as northward latitude shifts in vegetation, the melting of the ice sheets in Greenland and Antarctica, and GHGs releases from warmer oceans (in contrast to their absorbing them currently). Basically, carbon dioxide may be a lot more potent than we realise.
Three, the Summary’s highest estimation for sea level rise is roughly half to little less than one metre by the end of the century (p 18). This is certainly a step up from the upper limit of 59 cm presented in the Fourth Assessment Report, but many feel that even this is too low. It needs to be understood that 20th century sea level rise was largely linear because its main sources were expansion due to warmer waters and glacial melting. The main sources of 21st century sea level rise will be melting and ice flows from the great ice sheets on Greenland and Antarctica, a non-linear process. The world’s most famous climate scientist James Hansen has been saying repeatedly that “non-linear ice-sheet disintegration should be expected and multi-metre sea level rise [is] not only possible but likely”. It is too early to say whether it is the start of a non-linear trend, but the sharp rise in ice sheet melt five-six times in this decade mentioned above should set warning bells ringing somewhere. The extent of sea level rise has obvious implications for the extent of coastal erosion and flooding, the seepage of salt water into underground aquifers, and the extent of damage during storm surges, all of which are already being felt in India.
Finally, the urgency. It stems from the fact that we want to avoid crossing dangerous levels of warming, beyond which ecosystem feedbacks that usually cause further warming kick in simultaneously on a scale that would make it increasingly difficult for humans to control the process. Having a 50% probability of limiting warming to 2 °C, the Summary says, needs us to limit further emissions from now until the end of the century to little over 1,100 billion tonnes of CO₂, and we are galloping at over 30 billion tonnes a year. Emitting 1,300 billion tonnes would reduce the likelihood to 33% (p 20). As it is, an increasing number of scientists and ecologists have been saying that the 2 °C benchmark is way too high, some by looking at historical palaeoclimatic evidence, others at the severity of current impacts. The mood heading into climate negotiations in the 19th Conference of the Parties at Warsaw was one of low energy and expectations, whereas the latest Summary makes clear that the urgency is as pressing as ever. How bad climate impacts will be beyond the mid-century depends crucially on the world urgently shifting to a development trajectory that is clean, sustainable, and equitable, a notion of equity that includes space for the poor, for future generations and other species. Another reason to cut emissions urgently is the long-term implications of what we are doing; temperatures do not decline significantly for a thousand years after emissions stop (Solomon et al 2009). The sooner we cut back emissions now, the less pain we will bequeath to generations of the foreseeable future.