Pearls and Irritations

The climate crisis is much more severe than most people and politicians realise.

Most information, education and media reporting around climate change (global heating) focuses on reducing our annual emissions to a target based on a ‘trajectory of progressive reduction’, and eventually ‘net’ zero annual emissions by 2050 or some other date.

But this ignores the reality that it is the concentration of greenhouse gases in the atmosphere and their contribution to radiative forcing in real time that actually drive global heating.

Also, it’s not just CO2 that matters. The IPCC found that real time heating in the decade from 2010 to 2019 from relatively short-lived but very climate-active methane contributed more than half as much heating as CO2, even though its atmospheric concentration was much lower. But CO2 remains in the atmosphere for a very long time: much of it will still be in the atmosphere for more than 100 years, as shown below.

This article highlights some key insights that should underpin climate policy.

Every tonne of emissions adds to global heating and the longer it is in the atmosphere the bigger its cumulative impact

When we refer to our annual emissions in reports on climate change, it sends an unstated message that this is the most important indicator of our performance – and if annual emissions are declining towards ‘net’ zero by 2050, that is sufficient action. It’s not. As I pointed out to some young students recently, much of the emissions we release today will still be heating the planet when they are grown up and have kids of their own. This reality is illustrated by Figure 10 from the IPCC AR6 WG1 shown below as Figure 1.

A disadvantage of the way the data are presented in the IPCC graph is that the horizontal axis shows the cumulative emissions, rather than the time period when the emissions occurred. This means it is not easily linked to most of the graphs of emissions over time. Figure 2 shows my analysis from public data of the correlation between temperature change and cumulative emissions over time since 1900. It also shows how global heating correlates much better with cumulative emissions than with annual emissions.

Figure 2. Correlations between cumulative and annual CO2 emissions over time. Source 

This method of presenting emission data may be more effective in emphasising the need for urgent and substantial reductions in emissions if we are to slow, then stabilise global temperature increase.

Many governments and industries are promoting future technology developments such as nuclear power, green hydrogen and carbon capture and storage that will take decades to implement as solutions. These approaches will allow cumulative emissions to continue to grow, driving higher concentrations of greenhouse gases. We need to focus attention on short-term action. Today’s emissions will drive heating for many years.

In a recent presentation, I also tried to make this point by comparing Victoria’s recent annual emissions to its cumulative emissions over the same period, as shown in Figure 3.

Figure 3. Victoria’s annual greenhouse gas emissions and its cumulative emissions, which drives the concentration of greenhouse gases in the atmosphere and is the underlying driver of climate change.Real-world heating impacts of different gases

Our continuing use of 100-year Global Warming Potentials when reporting emissions perpetuates a significant distortion. Some gases have far higher short-term heating impacts than CO2. In the 1980s, when climate change looked like a long-term challenge and CO2 dominated global heating, this may have seemed like a reasonable metric. But now we face the serious risk of runaway global heating within decades and, as outlined earlier, emissions now and over the next few years influence that risk.

The IPCC highlighted this issue in the WG1 Summary for Policy Makers, as shown in Figure 4. Clearly, over the decade from 2010, methane contributed more than half as much to global heating as CO2, despite its much lower concentration in the atmosphere.

At a minimum, official reports should now regularly report 20-year GWP data or heating impact to 2050 as well as 100-year GWPs, so that appropriate priority is given to urgent action to cut emissions of gases that are very active over the period to 2050. Provision of these indicators, with associated explanation of their significance, is important in framing and implementation of appropriate policies and programs.

There is also a case for reporting of the lifetime climate impacts of decisions such as approvals of new fossil fuel projects and major industrial investments, presenting both 20-year and 100-year cumulative impacts. In my 2023 submission to the Climate Change Authority’s consultation on target setting, I made this point, as well as proposing regular reporting of Scope 3 emissions (both upstream and downstream) associated with Australian activities. It is important for Australians to recognise the upstream impacts of products and services we import, as well as the impacts of customer activities such as burning of our fossil fuel exports.

Figure 4. Observed real-world global heating over the decade from 2010. Source p.7

The need to drive urgent emission reduction is even greater than outlined in the above analysis. The graph in Figure 5 shows that the short term heating impacts of all major greenhouse gases are much higher than their average 100-year Global Warming Potential impacts. If we want to avoid runaway climate change in the next decade or two, the urgency of strong action is even greater. Every tonne of emission reduction does matter – and the sooner the reduction occurs, and absorption of greenhouse gases from the atmosphere occurs, the better for humanity’s future. Or the less disastrous our future will be.

Figure 5. Real time emissions of major greenhouse gases over time. Conventional carbon accounting focuses on 100-year Global Warming Potentials, but impacts in early years are above the 100 year average. Actual impacts in early years after emission are much higher, so the sooner we cut emissions the lower the cumulative climate impact over the next few decades.

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