Global climate change targets and terminology

Reading Time: 4 minutes

The Scottish Government released their annual Climate Change Plan (CCP) monitoring report at the end of May 2023. This is a statutory requirement set out in the Climate Change (Emissions Reduction Targets) (Scotland) Act 2019 and is the third progress report since the CCP update in 2020. Alongside this, the Scottish climate change adaptation programme: progress report 2023 was released, another annual progress report, this time related to climate change adaptation policy. To coincide with these, SPICe is publishing a series of blogs on climate change terminology, targets and impacts in Scotland.

These blogs are designed to raise awareness of climate change policy in preparation for the publication of the Scottish Government’s draft Climate Change Plan later in 2023.

Degrees of difference: the rate of global warming and the factors affecting it

While the Intergovernmental Panel on Climate Change (IPCC) is clear that it is ‘unequivocal that human influence has warmed the atmosphere, ocean and land’ it is useful to consider the current evidence around the rate of change and how it is communicated.

At the 27th Conference of Parties on climate change (COP27) (November 2022) there was much discussion about what level of global warming can be expected and whether it was still feasible to avoid more than a 1.5oC increase (an important target set at the UN climate negotiations in Paris 2015). At the time, recent observations recorded that slightly above 1oC of warming has already occurred and that there will be more (potentially much more).

The mainstream reporting of the science of global warming inevitably presents a simplified description of what is happening. For example, estimates of the level of warming include a range of uncertainty and some methodological context. The latest IPCC Physical Science Report states that global surface temperature was 1.09oC higher in 2011-20 than 1850-1900 (an ‘approximation of pre-industrial conditions’), and the range of uncertainty around this was 0.95 – 1.20oC. This finding is translated (reasonably enough) to ‘there has been 1.1oC of global warming’.

Within these changes there are a variety of natural factors (not human induced) that influence the climate, such as the cyclical climate fluctuations termed El Niño / La Niña. These factors mean that even as greenhouse gas (GHG) emission concentrations steadily increase, there isn’t a precise progression to higher temperatures. Globally, years are typically warmer during El Niño, and cooler during La Niña.

Despite these variations, however, viewed over a longer timescale the upward trend is clear; ‘each of the last four decades has been successively warmer than any decade that preceded it since 1850’ (essentially when records began). It is also worth noting that recent years have seen the occurrence of the La Niña phase, with a switch to El Niño expected to potentially start this year.

Feedback, tipping points and cascading effects

Further uncertainty in the rate of change is caused by potential greenhouse gas feedbacks, and the related concept of tipping points. A well-known example of feedback is when rising temperatures melt permafrost (particularly around the Arctic) which releases greenhouse gas emissions resulting in further warming. These feedback effects are one of ‘the dominant sources of divergence’ in model projections, with the potential that feedbacks could result in 25% more warming than the main IPCC projections.

There is also the potential for ‘tipping points’ to be reached – that is, the gradually increasing impacts of climate change could result in large, self-sustaining changes (changes that continue even if all emissions ceased). While there are a variety of possible tipping point events one recent study suggests there are four tipping points that are ‘likely’ at 1.5oC warming

  • Greenland and West Antarctic ice sheet collapse,
  • Low latitude coral reef die-off
  • Boreal permafrost thawing.

While these tipping points may not occur abruptly (complete ice sheet melting could take thousands of years) the change may be very difficult to reverse (ice sheet reformation would also take thousands of years). The changes are, therefore, sometimes referred to as irreversible, with the complete melting of the Greenland and West Antarctic Ice sheets also having the potential to raise sea levels by about 10m.

Another important consideration with climate change impacts are cascading systemic effects – ‘negative, compounding feedback loops’. The premise here is that there are initial or direct impacts of climate change like storms, drought, and heatwaves, but that these lead to further systemic impacts (physical and socio-economic). An example of cascading socio-economic impacts could be, heatwave causes drought, results in crop failure, leads to poverty and conflict / migration.

It is in part due to the uncertainty around tipping points, feedback loops and cascading effects that climate scientists feel we should err of the side of caution when it comes to planning emission reductions and climate adaptations (progress mitigation and adaptation measures at greater pace). 

There is also considerable regional variation to climate change, and its impacts. For example, land warms more quickly than ocean surfaces, with recent estimates of 1.59oC and 0.88oC increases respectively (higher in 2011–2020, than 1850–1900). The Arctic is also regularly highlighted as an area which is facing higher than average global warming. It is warming twice as fast as the global average, with a potential complete loss of sea ice in the summertime by the middle of this century.

Image of the world map showing the different levels of climate change temperature variation across the world

Image source: UK Met Office

Recent research from the World Meteorological Organisation sets out that global surface temperature is likely to be 1.5oC above preindustrial levels in at least one year of the next five years. This does not, however, mean that the Paris Agreement target has been broken, as this is measured over a longer time frame (rather than a single year).

In response to the changing climate, many countries have put in place ambitions for net zero emissions by a certain date and a follow-on blog considers what is meant by net zero emissions and what might happen once net zero is achieved. While 1.1 or 1.5oC may seem like relatively small changes in global average temperatures, they can result in significant changes to local environments The expected impacts of different levels of global warming for Scotland are considered in another SPICe blog.

Niall Kerr, Senior Researcher, Climate Change and Net Zero