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looking ahead

Our future climate depends on lower emissions - how big of a change would bring a real impact?

A major report has set out five possible climate scenarios, including a significant reduction in carbon emissions.

THE LESSON FROM the major climate report released today is that sweeping actions need to be taken to combat the climate crisis, but that it’s not too late to make a difference.

The report from the Intergovernmental Panel on Climate Change (IPCC) outlines potential future scenarios for the climate – and if emissions are reduced, how some of the worst effects of the climate crisis can be slowly reversed.

The key action identified is reducing carbon dioxide and greenhouse gas (GHG) emissions.

Climate change in this century depends on our level of emissions, how much global warming is caused by them, and how the climate system responds to that warming, the report found.

Different social and economic developments will lead to significantly different emissions of carbon dioxide, greenhouse gases and air pollutants for the rest of the century.

For global surface temperature to stabilise, carbon dioxide emissions need to reach net zero.

Speaking at a press conference for the release of the report this morning, IPCC chair Dr Hoesung Lee said that “strong, rapid sustained reductions in carbon dioxide and other greenhouse gas emissions will be required to limit global warming”.

Without those reductions, limiting global warming to 1.5 degrees Celsius will not be possible.

However, co-chair of the report’s working group Valérie Masson-Delmotte said that “if we rapidly reduce greenhouse gas emissions and if we can reach global net zero CO2 emissions by 2050, it is extremely likely that we can keep global warming below two degrees”.

“If we do this, it is more likely than not that temperature would gradually decline to below or around 1.5 degrees Celsius by the end of the century,” she said.

Five forecasts

The report sets out five potential future scenarios for the climate.

Which of them becomes reality depends on our level of emissions over the coming years and whether they’re very high, high, medium, low or very low.

  • High and very high: GHG and CO2 emissions that double by 2100 and 2050
  • Intermediate (medium): GHG emissions and CO2 emissions remaining at current level until middle of the century
  • Very low and low: GHG emissions and CO2 emissions declining to net zero around or after 2050 followed by net negative CO2 emissions.

Scientists expect that under any of the scenarios, global surface temperatures will continue to increase until at least the middle of the century.

But if we reduce our emissions to low or very low, we could gradually reverse the increase in those temperatures.

Under the very low emissions scenario, the average global surface temperature from 2081 to 2100 is very likely to be higher than from 1850 to 1900 by between 1 and 1.8 degrees Celsius, compared to 2.1 to 3.5 degrees or 3.3 to 5.7 under the medium or very high models.

Scenarios surface temperature How surface temperatures will rise depending on carbon emissions IPCC IPCC

In the very high or high scenarios, a rise in warming of two degrees Celsius – which is considered a benchmark that should not be crossed – would be exceeded.

It would also very likely be exceeded with medium emissions.

However, if emissions are low, it’s unlikely that threshold would be surpassed – and it’s extremely unlikely if they’re very low.

The difference between global warming rising by two degrees Celsius or less and rising by four degrees Celsius has significant implications for weather events.

At four degrees, hot temperature extremes (that would occur once every 10 years in a climate without human influence) would occur 9.4 times more frequently and be 5.1 degrees hotter.

For heavy one-day precipitation events that occurred once in 10 years on average in a climate without human influence, they would occur 2.7 times more often and be 30.2% wetter.

Agricultural and ecological droughts that occurred once in ten years on average across drying regions in a climate without human influence would be 4.1 times more frequent.

In contrast, at a temperature rise of two degrees, hot temperature extremes would be 5.6 times more frequent and 2.6 degrees hotter.

Heavy precipitation would happen 1.7 times as often and be 14% wetter and droughts would be 2.4 times as frequent.

In terms of the water cycle, precipitation and water flows are expected to become more variable from year to year and within seasons as the temperature rises, but with less severity under the lower emissions scenarios.

With very low emissions, annual global land precipitation (the amount of rain, hail and snow that falls over land in a year) would increase by 0 to 5%, but with very high emissions, it would increase by 1 to 13%.

Warming IPCC The contribution of different emissions to temperature increases under the five potential scenarios IPCC IPCC

“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,” the report states.

Reductions in methane emissions would also limit the warming effect resulting from declining aerosol pollution and would improve air quality, it says.

Relative to the high and very high models, “scenarios with low or very low GHG emissions lead within years to discernible effects on greenhouse gas and aerosol concentrations, and air quality”.

Speaking to The Journal, Peter Thorne, a professor at Maynooth University and one of the authors of the report, said that achieving a low-emissions scenario will require shifts in policies and in individual behaviours.

Individual choices could look like buying an electric car instead of a petrol or diesel one and taking a holiday within Ireland instead of travelling abroad, he said.

For governments, it means putting in place “policy frameworks, legal frameworks, fiscal frameworks, incentives, and disincentives” that reduce emissions. 

Coastal damage in Ireland 

In Ireland, according to a report published last year, more than 70,000 addresses will be impacted by coastal flooding by 2050 as a result of climate change.

These estimates are based on a 2 degree rise in global temperatures leading to a rise in sea levels, increased storm events and more extreme coastal flooding. 

The report, published by Gamma Location Intelligence, found that counties Louth, Clare, Limerick, Dublin and Galway are likely to be most affected by coastal flooding.

Almost 1 in 5 addresses in Louth and 1 in 8 in Clare are likely to experience coastal flooding by the middle of the century.

The report also notes that Dublin will be the most affected county in terms of the number of homes and businesses affected.

An estimated 23,435 addresses in the county will be impacted by coastal flooding, the report says, with buildings in areas such as Clontarf, Portmarnock, Donabate and Sandymount at a greater risk, particularly during storm events.

The study found that the property costs associated with an extreme coastal flooding event in Ireland are estimated to be over €2 billion, with estimated property damage of upwards of €600,000,000 in Dublin alone.

This does not include the costs associated with infrastructure damage. 

With reporting by Emma Taggart 

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