IPCC Second Assessment -- What we can learn from a 30 year old report (WG1)

The Intergovernmental Panel on Climate Change (IPCC) was established in 1988. It produced its Second Assessment Report in 1995. 3 decades later, it's worth asking, how far have we come since then?

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Working Group I (The Science)

One need only look at the structure of the Summary to get a broad snapshot of what was known then. Greenhouse gas concentrations had continued to increase since the previous report, aerosols were known to lead to cooling in some areas, the climate was known to be changing and there was reason to believe it was changing due to human activities. (This is an interesting nuance -- detecting a change is not the same as attributing it to human activities -- Gavin Schmidt elaborates on this here.) The climate was expected to continue to change and many uncertainties still remained.

It was known quite clearly that -- "Many greenhouse gases remain in the atmosphere for a long time (for CO₂ and N₂O, many decades to centuries)..". The greenhouse gases that were emitted while this report was being written are still hanging around and trapping heat in the atmosphere today. The greenhouse gases that are being emitted by you and me today will continue to affect us for the rest of our lifetime.

A clear distinction was also made between greenhouse gases and aerosols. While greenhouse gases always lead to warming, the IPCC mentioned that:

"Tropospheric aerosols (microscopic airborne particles) resulting from combustion of fossil fuels, biomass burning and other sources have led to a negative direct forcing.."
"Locally, the aerosol forcing can be large enough to more than offset the positive forcing due to greenhouse gases." [Positive radiative forcing = warming]
"In contrast to the long-lived greenhouse gases, anthropogenic aerosols are very short-lived in the atmosphere, hence their radiative forcing adjusts rapidly to increases or decreases in emissions."

This is a very important distinction which hasn't adequately permeated the climate conversation in India. As we hope to make progress on the air pollution front, we must expect warming to increase due to the absence of these pollutants. Any broad environmental view must take into account expert opinions about both climate change and air pollution -- that is, two different viewpoints. And finally, while we can hope to make quick progress on the air pollution front, we cannot have the same hopes about climate change. A dismal corollary is -- if we cannot make quick progress on the air pollution front, there is little hope to make progress on the climate change front.

"The balance of evidence suggests a discernible human influence on global climate"

The evolution of the IPCC's language regarding attribution of climate change to human activities is very interesting. I remind the reader of the distinction between detection and attribution. Detection means saying "something is likely/definitely amiss". Attribution means saying "it is likely/definitely amiss due to human activities".

In this regard, the First Assessment Report (1990) had said:

"The size of the warming over the last century is broadly consistent with the predictions of climate models, but it is also of the same magnitude as natural climate variability."
"The unequivocal detection of the enhanced greenhouse effect from observations is not likely for a decade or more .."

i.e. neither detection nor attribution were possible in 1990.

The Second Assessment Report went a bit further:

"Most of these studies have detected a significant change and show that the observed warming trend is unlikely to be entirely natural in origin."
"Our ability to quantify the human influence on global climate is currently limited because the expected signal is still emerging from the noise of natural variability, and because there are uncertainties in key factors."
"Nevertheless, the balance of evidence suggests that there is a discernible human influence on global climate."

i.e. detection was possible and attribution was emerging in 1995.

Source: Technical Summary, WG1, SAR

The figure above shows two things clearly: that first, models which took into account only greenhouse gases (and not aerosols) simulated temperatures that were too high when compared to the observations. On the other hand, models which take into account both could simulate temperatures that matched observations. Secondly, the emerging signal of warming was beginning to be clear in the upward rise of the last few decades. Note that this figure was produced 30 years ago and is, in fact, available from the scanned copy of the original report. Thus, even "primitive" global climate models could match observations fairly well by the 90s. This is due to both the development of climate models and the strong anthropogenic signal.

Some numbers and trends

The IPCC noted in 1995 that:

Global sea level had risen by 10-25 cm over the past 100 years
They expected a 50 cm rise from then till 2100 in global sea levels
They expected a 1-3.5℃ rise by 2100 compared to 1990
Both temperatures and sea levels were expected to continue to rise beyond 2100 even if greenhouse gas concentrations were to be stabilized by then

30 years after

30 years ago, India was led by P. V. Narsimha Rao. The Indian Cricket Team was led by Mohammad Azharuddin. Sushmita Sen and Aishwarya Rai had won international beauty titles the previous year. Bombay turned to Mumbai. Dilwale Dulhania Le Jayenge was released, Maratha Mandir was beginning its epic run of screening it. The internet and cellphones were arriving. Simply put, 1995 was a long, long time ago.

Climate science has made tremendous progress in these three decades. We have unequivocally detected and attributed anthropogenic climate change. There is no longer a question of whether there is a problem and whether the solutions lie in our (human) hands. We have holistic models that can connect climate information to social and economic information. The resolution and complexity of climate models has improved substantially, affording us detailed and regional information about potential impacts. We have tools for quantifying costs and benefits of climate action. Thanks to the internet and to cellphones, we certainly have the technological tools for accessing, visualizing and disseminating climate information rapidly and effectively.

In many ways, however, the vast majority of people seem to be stuck in 1995, where detection is emerging in their minds (i.e. they are beginning to notice that something is awry) but attribution (and hence, taking responsibility) is still not on the horizon. There is indeed a small proportion of people who are working hard and keeping things from being not as bad as they would have been otherwise. And unsurprisingly, there is a bigger proportion who claim to be helping but well ... we should talk about greenwashing in another post.

What stops us from making real progress on this front?

Source: Our World in Data

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