The Pre-Industrial Baseline
The Intergovernmental Panel on Climate Change (IPCC) has just released the ‘Summary for Policymakers’ for its Sixth Assessment Report (AR6). We will work through its conclusions and recommendations in future posts. This is an important report. However, as is usual with IPCC reports, it is not an easy read. The following is the opening paragraph.
This Synthesis Report (SYR) of the IPCC Sixth Assessment Report (AR6) summarises the state of knowledge of climate change, its widespread impacts and risks, and climate change mitigation and adaptation. It integrates the main findings of the Sixth Assessment Report (AR6) based on contributions from the three Working Groups, and the three Special Reports. The summary for Policymakers (SPM) is structured in three parts: SPM.A Current Status and Trends, SPM.B Future Climate Change, Risks, and Long-Term Responses, and SPM.C Responses in the Near Term.
It is hardly attention-grabbing.
But first, I would like to consider the widely used term ‘pre-industrial’ baseline.
The following chart was provided by the UK Met Office. It shows temperature changes compared to the 1951-1980 average. The first thing a person notices is the rapid increase in global temperatures since about 1970. If the trend continues, then we reach the 1.5°C threshold sometime around the year 2040.
But the chart provides two other insights. First, we see that, in the period 1940 to 1970 temperatures hardly changed at all. Yet this was a time on growing industrial activity around the world. That energy for that activity came from fossil fuels, which generate greenhouse gases.
The second insight is to do with the period 1880-1910. Temperatures went down during that period, even though industrialization continued its relentless growth. Presumably factors other than human activity were the cause of that temperature decrease.
One of the themes of this site, and of the books that we are writing, is that climate change is an immensely complex process — one that involves many feedback loops, many of which we do not fully understand, and some of which have not even been identified. The chart shows that many factors are at play when it comes to climate change. Some of these factors can be sudden — volcanic eruptions and meteor strikes are examples. Other feedback factors, such as increased uptake of carbon dioxide by plant life, are more gradual.
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