No more heatwaves, less snow and more rain

The Intergovernmental Panel on Climate Change (IPCC) continues to ask the question: What will the future climate look like under several different emission scenarios?

In a regular series of reports dating back to 1990, scientists have given the same answer: the more greenhouse gases we emit, the warmer the world will be. The repetition becomes boring. The only difference over the past 30 years is that as data accumulates, science advances, models improve, and computers get more powerful, there is more confidence and more details in this answer.

What was “probable” just a few years ago is now “practically certain”, to the point that UN Secretary General António Guterres has called the latest AR6 report a “red code for humanity”. He found that human activities have unequivocally warmed Earth’s climate across the planet, and that these changes are widespread, rapid and intensifying.

Advances in climatology and high-performance computing have enabled the continuous improvement of climate models. In 1990, climate simulations could only offer rough representations of the atmosphere, without the possibility of taking into account dynamic oceanic or terrestrial processes.

In contrast, the latest report assesses large sets of high-resolution models that couple all components of the real climate: atmosphere, ocean, land / vegetation, and sea ice. Today’s climate models synthesize and digitally represent all of the climates. latest scientific knowledge on radiation, cloud microphysics, turbulence and other processes that together determine climate.

As a result, our ability to predict the climate response to any particular future emissions scenario (or “forcing”) has become much more robust. The main question now is, what will these emissions really be?

For any specific trajectory of future greenhouse gas emissions, climate models project what the climate response would be. We speak of climate “projections” instead of “forecasts” because the climate over the next few decades depends to some extent on human-controlled emissions, and we cannot be sure how humans will choose to. ‘exercise this control.

Ireland’s contribution

Ireland contributes in particular to the IPCC reports through its participation in a consortium of several northern European countries that are developing and running one of the 50 or so global climate models that feed into the IPCC assessments.

The Irish Center for High End Computing (ICHEC) has conducted centuries of global climate simulations with the “EC-Earth” climate model. As a “model of the earth system” it represents all of the most relevant physical processes that operate in and between the atmosphere, ocean, land surface and sea ice. The simulations go from the historical past, so that model performance can be compared to actual climate records, until the end of the 21st century. This work is supported by the EPA, the Met Éireann and the Marine Institute.

Over 50 different global climate models have been developed by different research centers around the world, including Ireland, through ICHEC and the Met Éireann. Like Formula 1 cars, they can share certain parts, but each is also different in its own way.

Their real strength, however, is that they are collectively organized to each perform the same simulation experiments. As far as the particular design of each model allows, they all use the same initial configuration, the same boundary conditions and the same future emission scenarios. Collectively, they generate sets of several thousand sample climates for each scenario.

This number is high enough to generate high confidence that something close to the full range of possible climates is being captured. Dr Pangloss de Voltaire would be impressed. Multi-model sets like this are great examples of the whole greater than the sum of its parts.

These coordinated climate simulation projects also reflect how climate research has become ‘big science’, without a single person or even a single institute being able to do it all. The ICHEC simulations alone consumed tens of millions of computer core hours, and the resulting datasets occupy more than 1.5 petabytes (equivalent to the storage capacity of well 1,500 modern laptops. endowed).

The potential for more extreme events

Almost every model from 30 years ago to now predicts that the world will continue to heat up if greenhouse gas emissions continue on their current path. An average warming of 2 or 3 degrees may not seem like much, as temperatures can vary much more than that from day to day. However, even this level of warming is likely to cause widespread and even dramatic changes in ice cover (especially in the Arctic) and in the natural world of plants and animals.

Additionally, a changing climate tends to alter the full range of expected weather conditions, not just the average. Even more dramatic future changes are projected for the extremes, or “tails”, of the frequency distributions of each climate sample. Thus, a rain event so intense that it only occurred once every 100 years or so in the past, may occur every 20 years in the future. Likewise, long, deep freezes (such as during the winter of 2010-2011) could become even rarer in a warmer future world.

What does this mean for Ireland?

Scientists at ICHEC supplemented the global projections with another set of regional simulations (each nested within a larger global simulation) to provide a set of ultra-high-resolution future climate projections for Ireland. These provide a wealth of detail on the likely characteristics of Ireland’s future climate. Selected results of this to study are that by the middle of this century (2041-2060) we should expect:

– Temperature increase of 1.0-1.6 degrees (compared to 1981-2000) with the largest increases in the east;

– More frequent summer heat waves, especially in the south;

– About 50% less frost and ice days;

– More variable precipitation, with drier periods and more intense precipitation episodes;

– A decrease in snowfall of 50 percent or more;

– Weaker surface winds, as well as a reduction in the energy content of the wind by 120 meters (height of the turbine) in all seasons;

– The annual growing and grazing seasons are expected to lengthen by 12 to 16 percent. Likewise, crop heat units and growing degree days for a range of crops (and pests) are likely to increase dramatically.

The capacity of supercomputers has increased by more than seven orders of magnitude, or a factor of 10 million, over the past 30 years. This has enabled advances in climate science that would have been unthinkable even as recently as 1990. Given the computational resources currently available and other scientific advances, model simulations can provide very accurate indicators of our climate.

The level of detail and consistency achieved gives confidence in these projections and allows an ever more convincing evidence-based consensus to emerge that humans are forcing rapid climate change in well-understood ways.

How to respond to this consensus now is a question primarily for governments (since they can have the most impact) as well as for individuals.

Dr Enda O’Brien and Dr Paul Nolan are based at the Irish Center for High End Computing in Galway