Acceleration of Climate Change Trends Revealed

This article reviews the World Meteorological Organisation’s (WMO) Report^[1] to highlight the lack of positive action, and also show the effects on UN Sustainable Development Goals (SDGs). If we are able to make real progress on climate change this will also lead to real and welcome improvement in the achievement of SDGs.

Atmospheric composition

The Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) made clear that the abundance of greenhouse gases (GHGs) since the pre-industrial period is a major reason for observed global warming.

The key GHGs, carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O), have both anthropogenic (human-generated) and natural sources. These GHGs allow solar radiation to reach the Earth’s surface, but then reflect rising infrared radiation back to the surface, further heating the planet. This is known as radiative forcing.

CO₂ is the most important of the anthropogenic GHGs, contributing about 66% of the radiative forcing caused by these long-life GHGs (LLGHGs), and about 81% of the increase over the 2011-2020 decade.

Before the start of the industrial era, atmospheric CO₂ had been largely stable, at around 280 parts per million (ppm). This has increased over each of the last three decades, averaging 402 ppm over 2011-2020. This is primarily due to fossil fuels, deforestation and changes in land-use.

About 55% of CO₂ anthropogenic emissions are absorbed by the ocean and by sinks on land, e.g. forests. This absorption level has been stable over the last three decades with the oceans removing 25% and land 29% from 2010 to 2019.

CH₄ contributes about 16% of radiative forcing by LLGHGs. About 40% of CH₄ is from natural sources (wetlands, termites) and 60% is anthropogenic (ruminants, rice agriculture, fossil fuels, landfills and biomass burning).

Before the industrial era, the CH₄ concentration was around 730 parts per billion (ppb). Despite some variability, CH₄ concentrations have increased over each of the last three decades to 1850.2 ppb in 2011-2020, an increase of over 150%. This increase has generally been driven by emissions from agriculture, waste and fossil fuels, with wetlands contributing to a lesser degree.

N₂O accounts for about 7% of radiative forcing by LLGHGs. N₂O is generated by both natural (64%) and anthropogenic (36%) sources, e.g., oceans, soils, biomass burning, fertilizers and various industrial processes. N₂O is particularly potent, as its climate impact is nearly 300 times that of an equal quantity of CO₂ emissions.

Prior to industrialisation, N₂O concentration was around 270 ppb. Over the last three decades, growth has continued to 328.6 ppb in 2011-2020, particularly through the excess use of nitrogen fertilisers.

Emissions from all three GHGs must decrease substantially and sustainably, with CO₂ emissions decreasing to near-zero, if the Paris Agreement temperature goal of 1.5^oC is to be met.

Global temperature

The average temperature in the period 1850 to 1900 is taken as representative of the pre-industrial temperatures. The IPCC defines the crossing of a threshold (e.g., the Paris Agreement 1.5^oC) as the midpoint of the first 20-year period with mean temperatures higher than that threshold.

The global mean temperature for 2011-2020 was about 1.10^oC above the 1850-1900 level and was the warmest decade on record for most regions. The region showing the highest increase over the previous decade was the Arctic.

Oceans

About 90% of Earth’s heat is stored in the oceans, measured through Ocean Heat Content (OHC). Since 2006, there is now near-global measurement coverage to a depth of 2kms. Ocean warming is measured in watt/square metre (Wm^-2).

Ocean warming has been particularly strong over the past two decades; the warming rate for 2006-2020 was around 1.0 Wm^-2, compared to 0.6 Wm^-2 for the period 1971-2020.

Sea levels continued to rise during the 2011-2020 decade, with some evidence of acceleration. The global mean sea level (GMSL) rise for 2001-2010 was 2.9 mm/yr and increased to 4.5 mm/year. The GMSL acceleration is mostly due to the increased rate of loss of the Greenland ice sheet and, to a lesser extent, faster glacial melting and ocean warming.

The oceans have continued to take up an average of 25% of (increasing) anthropogenic CO2 emissions. This has resulted in increased acidification, making it more challenging for marine organisms to build and maintain shells and skeletons.

Cryosphere

The cryosphere is the frozen water on Earth, e.g., glaciers, sea, snow, lake ice, and frozen ground (permafrost).

Glaciers thinned on average each year over the 2011-2020 decade, by 1m pa over their entire surface. This was measured across 42 reference glaciers with at least 30 years of measurements. Glacial retreat (elevation changes) is also very evident.

Sea ice is substantial in both Arctic and Antarctic regions. Arctic sea ice declined over the 2011-2020 decade, particularly during the summer melt. The Arctic sea ice covered 4.37m km² as a mean seasonal minimum during the decade, which was 30% lower than the average for the 1981-2010 period. As with the summer minimum, the winter maximum measurements for each year of the 2011-2020 decade were below the 1981-2010 average.

‘Old ice’ (ice that has been continuously frozen for four years or more) has decreased dramatically; from 33% of the total Arctic ice cover in March 1985 to below 10% in 2010, and to 4.4% in March 2020.

Antarctic sea ice has not been so clearly affected, partially due to the relatively weak warming trend in much of the Southern Ocean (see the first diagram above).

According to the limited data that is available, mostly from Alaska, indicates that permafrost (ground that remains at or below 0^oC for two consecutive years) temperatures have risen across the decade at a mean trend of 0.6^oC / decade. Dangers from permafrost melting include ground subsidence or landslides, and the release of GHGs from the previously-frozen organic carbon.

Extreme events and impacts on UN Sustainable Development Goals (SDGs)

For virtually all extreme heat events in the 2011-2020 decade, attribution studies have shown that anthropogenic climate change has significantly increased the likelihood of these events.

Heat waves were responsible for the highest number of casualties while tropical cyclones caused the most economic damage. The number of casualties has declined due to improved early warning systems while economic losses have increased.

Progress on SDG 1: No Poverty and SDG 7: Clean Energy are the most frequently reported SDGs impacted by extreme events.

Closer to home, extreme events in Australia are noted:

• Extensive flooding in eastern Australia in 2011 / early 2012, with Brisbane having its highest flood levels since 1974.
• Drought in southern Australia between 2017 and 2019, with 2019 being Australia’s driest year on record. This contributed to extensive wildfires and the northern Murray-Darling Basin below 6% capacity in early 2020.
• The unprecedented bushfire season of 2019/2020 led directly to 34 deaths and a further 400 attributed to persistent smoke pollution. There were over 3,500 buildings destroyed with 65,000 displacements (generally pre-emptive evacuations).

Synergistic climate and SDG policy

The UN Secretary-General, Antonio Guterres said, “Climate action is the 21st century’s greatest opportunity to drive forward all the Sustainable Development Goals.”

The achievement of SDGs has been severely hampered by climate change. As an example, Hurricane Irma was a category 5 hurricane that crossed Antigua and Barbuda in Sept 2017. The value of destroyed assets and production disruptions amounted to around 9% of GDP, with impacts on poverty, housing (95% of houses on Barbuda damaged, 45% uninhabitable), tourism and transport, and biodiversity. Small Island Developing States (SIDS) are particularly impacted by extreme events.

This highlights the opportunity for action on climate change to also improve progress on SDGs, as noted by Secretary-General Guterres.

The clear message from the report is that more ambitious climate action is needed. A number of recommendations for actions by global policymakers on climate and sustainable development have been proposed:

1. Enhancing collective resilience against global crises.
2. Strengthening science-policy-society interaction.
3. Promoting institutional capacity-building.
4. Ensuring policy coherence and coordination to enhance synergies at all levels.
5. Developing a ‘framework for action’ to assist decision-makers achieve synergistic action.
6. Addressing the large investment goals to enhance necessary synergies and effective allocation of budgets.
7. Prioritising the role of synergies in the work of the UN, including improved systems for sharing information and cross-sectoral engagement.
8. Treating cities as opportunities for focusing on climate and development synergies as centres of population and economic activity.

References

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