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IPCC climate change report summary

The Intergovernmental Panel on Climate Change (IPCC) released its sixth assessment report (AR6) on climate change this week, as you probably know. I actually feel a little better after reading it, in part because it’s just better to know what the situation is. Our situation could be summarized as follows:

All is not lost but we absolutely need to change our habits, drastically and immediately.

Some media reporting leaves us with the feeling that we are doomed, which can dangerously make people feel like just not bothering anymore. The climate is changing for sure and it’s going to get even more extreme before this is over, but there’s a path forward for limiting it. So don’t despair.

Summary of the IPCC Report

When you go to the webpage for the IPPC sixth assessment report, you’ll face several options. The Summary for Policymakers (SPM) captures the essential findings in 42 pages – this is the report that most people will want. The Technical Summary (159 pages) is still a bit rough looking and the information overlaps with the SPM report, but it contains some crucial info, like the last figure in this post. The FAQs document (96 pages) is a good read and I have a section of highlights from it, later on. The full report is just under 4000 pages long and requires some patience to navigate 😉

Overall, this sixth assessment report (AR6) adds new data and improved climate models and it’s a significant update on the fifth assessment (AR5), which was released in 2013.

How much has the earth warmed since pre-industrial levels?

Measuring CO2 levels in the atmosphere is fairly straightforward, but measuring the average surface temperature of the earth is obviously a bit more complex. Variations in temperature (spatially, seasonally, annually) make it challenging to get an accurate number when looking at a small time window. First, a reminder of our goal from the Paris Agreement, signed by most countries in 2016:

The Paris Agreement aims is to limit the rise in mean global temperature at 2.0 °C above pre-industrial levels at most, and preferably 1.5 °C.

According to the latest IPCC report, the mean global surface temperature has already risen by 1.09°C above pre-industrial levels (i.e., compared to the average global temperature in 1850-1900) .

Here’s some more detail on that number: The global surface temperature was 1.09 °C higher in 2011–2020 than 1850–1900, with larger increases over land (1.59 °C) than over the ocean (0.88 °C). The average value of 1.09 °C is the IPCC’s best estimate on the temperature increase, with a range of 0.95 to 1.2 °C.

Our current climate situation

OK, so the earth has already warmed by around 1.1 °C, compared to a Paris Agreement target of 1.5 °C. Here’s some more information on temperature, oceans, and rainfall.

Global temperature

Global surface temperature has increased faster since 1970 than in any other 50-year period over at least the last 2000 years (high confidence). Each of the last four decades has been successively warmer than any decade that preceded it since 1850.

It is virtually certain that hot extremes (including heatwaves) have become more frequent and more intense across most land regions since the 1950s, while cold extremes (including cold waves) have become less frequent and less severe, with high confidence that human-induced climate change is the main driver of these changes.

The ocean

It is virtually certain that the global upper ocean (0–700 m) has warmed since the 1970s and extremely likely that human influence is the main driver. It is virtually certain that human-caused CO2 emissions are the main driver of current global acidification of the surface open ocean. Surface open ocean pH as low as recent decades is unusual in the last 2 million years (medium confidence)

The rate of ice sheet loss increased by a factor of four between 1992–1999 and 2010–2019. Together, ice sheet and glacier mass loss were the dominant contributors to global mean sea level rise during 2006-2018.

Floods and droughts

The frequency and intensity of heavy precipitation events have increased since the 1950s over most land area for which observational data are sufficient for trend analysis (high confidence), and human-induced climate change is likely the main driver. Human-induced climate change has contributed to increases in agricultural and ecological droughts in some regions due to increased land evapotranspiration (medium confidence).

Future climate scenarios

Various scenarios of future global CO2 emissions were modeled by the IPCC, as shown below. In the two scenarios shown in blue (SSP1-1.9 and 2.6), CO2 emissions are kept steady until 2025 and then reduced to a point where emissions are net negative in a few decades. The scenario in orange (SSP2-4.5) shows a small increase in our rate of CO2 emissions until around 2060 and then a gradual reduction. Then the scenarios in red (SSP3-7.0 and SSP5-8.5) involve CO2 emissions that continue to climb. So the blue scenarios show where we should be going, while our current CO2 emission trends are closer to the red scenarios.

Here is the IPCC’s prediction of what these scenarios will translate to in terms of global temperatures:

Compared to 1850–1900, global surface temperature averaged over 2081–2100 is very likely to be higher by 1.0°C to 1.8°C under the very low GHG emissions scenario considered (SSP1-1.9), by 2.1°C to 3.5°C in the intermediate scenario (SSP2-4.5) and by 3.3°C to 5.7°C under the very high GHG emissions scenario (SSP5-8.5). The last time global surface temperature was sustained at or above 2.5°C higher than 1850–1900 was over 3 million years ago.

Every additional 0.5°C of global warming causes clearly discernible increases in the intensity and frequency of hot extremes, including heatwaves (very likely), and heavy precipitation (high confidence), as well as agricultural and ecological droughts.

Here are some maps showing how the average increase in global temperature is predicted to play out – some areas will get a lot hotter.

Annual mean temperature change (°C), relative to 1850-1900. Across warming levels, land areas warm more than oceans, and the Arctic and Antarctica warm more than the tropics.

There are also various charts explaining how the frequency of rare climate events will increase. An extreme heatwave that used to occur about every 50 years is predicted to occur almost annually if the global temperature is allowed to increase by 4 °C. And it’ll be more intense (i.e., hotter), as shown in the lower chart.

Soil moisture will change radically, with some areas like the Mediterranean countries becoming extremely dry.

Some oceanic changes will continue no matter what, but to an extent that depends on our actions.

Past GHG emissions since 1750 have committed the global ocean to future warming (high confidence). Based on multiple lines of evidence, upper ocean stratification (virtually certain), ocean acidification (virtually certain) and ocean deoxygenation (high confidence) will continue to increase in the 21st century, at rates dependent on future emissions.

Mountain and polar glaciers are committed to continue melting for decades or centuries (very high confidence).

The Atlantic Meridional Overturning Circulation (AMOC) is very likely to weaken over the 21st century for all emission scenarios.

(Studies that track changes in that North Atlantic AMOC current have been in the news recently.)

IPCC FAQs on climate change

Can thawing permafrost substantially increase global warming?

In the Arctic, large amounts of organic carbon are stored in permafrost – ground that remains frozen throughout the year. If significant areas of permafrost thaw as the climate warms, some of that carbon may be released into the atmosphere in the form of carbon dioxide or methane, resulting in additional warming. Projections from models of permafrost ecosystems suggest that future permafrost thaw will lead to some additional warming – enough to be important, but not enough to lead to a ‘runaway warming’ situation, where permafrost thaw leads to a dramatic, self-reinforcing acceleration of global warming.

Could climate change be reversed by removing carbon dioxide from the atmosphere?

Removing more CO2 from the atmosphere than is emitted into it would indeed begin to reverse some aspects of climate change, but some changes [e.g., sea level rise] would still continue in their current direction for decades to millennia. Approaches capable of large-scale removal of CO2 are still in the state of research and development or unproven at the scales of deployment necessary to achieve a net reduction in atmospheric CO2 levels. CO2 removal approaches, particularly those deployed on land, can have undesired side-effects on water, food production and biodiversity.

What are short-lived climate forcers and how do they affect the climate?

Short-lived climate forcers (SLCFs) are compounds such as methane and sulphate aerosols that warm or cool the Earth’s climate over shorter time scales – from days to years – than greenhouse gases like carbon dioxide, whose climatic effect lasts for decades, centuries or more. It is therefore important to understand how SLCFs work and to quantify their effects. Because reducing some of the SLCF emissions, such as methane, can simultaneously reduce warming effects and adverse effects on air quality as well as help attaining Sustainable Development Goals, mitigation of SLCFs is often viewed as a favourable ‘win-win’ policy option. [See the next FAQ for more on this.]

What are the links between limiting climate change and improving air quality?

Climate change and air quality are intimately linked. Many of the human activities that produce long-lived greenhouse gases also emit air pollutants, and many of these air pollutants are also ‘short-lived climate forcers’ that affect the climate.

For example, some short-term ‘win-win’ policies that simultaneously improve air quality and limit climate change include the implementation of energy efficiency measures, methane capture and recovery from solid waste management and oil and gas industry, zero-emission vehicles, efficient and clean stoves for heating and cooking, filtering of soot (particulate matter) for diesel vehicles, cleaner brick kiln technology, practices that reduce burning of agricultural waste, and the eradication of burning of kerosene for lighting.

Can continued melting of the Greenland and Antarctic ice sheets be reversed?  How long would it take for them to grow back?

Some of the consequences of human-induced climate change will continue for a very long time, even if atmospheric heat-trapping gas levels and global temperatures are stabilized or reduced in the future. This is especially true for the Greenland and Antarctic ice sheets, which grow much more slowly than they retreat. If the current melting of these ice sheets continues for long enough it becomes effectively irreversible on human timescales, as does the sea level rise caused by that melting. 

Limiting Future Climate Change

From a physical science perspective, limiting human-induced global warming to a specific level requires limiting cumulative CO2 emissions, reaching at least net zero CO2 emissions, along with strong reductions in other greenhouse gas emissions. Strong, rapid and sustained reductions in CH4 emissions would also limit the warming effect resulting from declining aerosol pollution and would improve air quality.

This Report reaffirms with high confidence the AR5 finding that there is a near-linear relationship between cumulative anthropogenic CO2 emissions and the global warming they cause. Each 1000 GtCO2 of cumulative CO2 emissions is assessed to likely cause a 0.27°C to 0.63°C increase in global surface temperature with a best estimate of 0.45°C.

(A GtCO2 is a gigatonne of carbon dioxide, equaling 1 billion metric tonnes of CO2)

Here’s the total carbon budget (i.e., the amount of CO2 emissions allowed) that would keep us within the Paris Agreement limits of a maximum temperature gain of between 1.5 to 2.0°C. I’ve highlighted two numbers – total emissions of 300 GtCO2 would give us a good chance of staying below the 1.5°C limit. At the other extreme, emissions of 2300 GtCO2 would leave us with almost no chance of staying below the 2.0°C limit.

That CO2 clock started ticking at the beginning of 2020, and globally we emit around 40 GtCO2 per year. So we’ll have emitted around 80 GtCO2 by the end of this year – more than a quarter of our “safe” budget. The amount of CO2 that we emit globally is still increasing, despite announcements on commitments from government and corporate leaders.

This time factor is why, when I look at the companies like Amazon, I pay attention to the actual carbon footprint (which is increasing) rather than whatever future commitment that the CEO announces. The same is true for a major food corporation that I’ll be profiling soon.

The importance of methane to climate

Reducing our methane (CH4) emissions would help mitigate climate change – that’s not news – perhaps adding the words a lot would capture the newsworthy part. After the last IPCC report, it seemed likely that the oil and gas industry was about to be held responsible for the massive amounts of methane released, leaked, or burned as flares. Then Trump happened and fossil fuel companies were given free reign again to ignore methane leaks and to carry on fracking. There’s absolutely no excuse for this to be still going on and reminding your politicians of this is a worthwhile action.

The other two main contributors to methane emissions, as you can see from the chart below, are agriculture and waste management. To be more specific, that’s predominantly animal agriculture (meat and dairy) and poorly managed landfills.

The methane has a large impact on a shorter time scale (a decade or two) while CO2, which lasts much longer in the atmosphere, impacts climate for more than a century. Reducing methane emissions would significantly help to mitigate climate change because methane, although shorter-lived, has a much higher global warming potential than carbon dioxide. As the BBC pointed out this week, curbing methane helps to buy more time to deal with climate change.

Interestingly, some emissions – particularly sulfur dioxide and nitrogen oxides (NOx) – can actually help reduce warming. But these emissions cause other problems like air pollution and acid rain, so they aren’t a viable solution!

Here are key points from that chart:

  1. The sectors that produce a lot of methane (orange bars) – fossil fuel production, agriculture, waste management – have large contributions to climate change on a short time scale (10 years).  
  2. The sectors that produce a lot of CO2 (yellow bars) – fossil fuel burning, general industry, transportation, buildings – have large contributions to climate change on a long time scale (a century).
  3. Of the methane-producing sectors, the main ways that we can impact them are to buy less stuff (fossil fuel production and waste management) and switch to plant-based diets (agricultural methane).  

I’ll be covering both topics in the near future – for example, I’ll summarize some of the best vegan dairy brands that I’ve covered on Ethical Bargains. Stop grumbling, dairy-lovers, we need to start changing!

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