What does global average temperature increase of 1.5°C mean for coasts and deltas?

Source(s): Climate and Development Knowledge Network
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Marking the launch of the IPCC Special Report on 1.5C of global warming, Katharine Vincent caught up with Robert Nicholls, Professor of Coastal Engineering and Sally Brown, Senior Research Fellow, at the University of Southampton, to discuss the implications of 1.5°C of warming on coasts and deltas. Dr Brown was a lead author on the IPCC Special Report.

Why the IPCC Special Report on 1.5°C?

In 2015, governments committed under the Paris Agreement to hold ‘the increase in the global average temperature to well below 2°C above pre-industrial levels and pursue efforts to limit the temperature increase to 1.5°C above pre-industrial levels’. 2°C is widely accepted as a critical threshold, and sometimes referred to as a “planetary limit” and if temperature increases beyond this it is likely to cause transformations in ecosystems.

For policy-makers to weigh up the pros and cons and additional interventions to limit greenhouse gas emissions, they need to know how different impacts would be if we are able to limit temperature increase to 1.5°C. This was the motivation for the Intergovernmental Panel on Climate Change Special Report on “the on the impacts of global warming of 1.5 °C above pre-industrial levels and related global greenhouse gas emission pathways”.

How much will sea level rise?

How much sea level rises reflects how much the temperature increases, and how much temperature increases reflects our activities – and how many greenhouse gases we emit into the atmosphere. Since we don’t know what our future emission levels we be, we use different scenarios in our models. In a “worst case” scenario, if greenhouse gas emissions continue to rise, then temperature increase will be higher and we may find that sea levels rise by just over three quarters of a metre by 2100. In a best case scenario, if we manage to limit our emissions to the level that leads to only a 1.5˚C increase in temperature, then they will rise by 40cm – less than half as much.

The picture gets worse further into the future – under the worst case scenario we can expect to see an increase in sea level of 4 metres by 2300, compared to 1m if we can limit temperature increase to 1.5˚C.

What impact will this have on coasts and deltas?

Over 100 million people live in flood prone coastal areas today. By 2100, the number of people living in flood prone coastal areas is projected to rise up to 220 million. In our research in deltas in Asia we have seen the devastation caused by coastal flooding associated with cyclones – which damages road infrastructure and houses and can lead to erosion and salinization of soils, rendering land unsuitable for agriculture. In many small islands, sea level rise leads to loss of land and has caused people to have to move – in the Maldives the government has already created a new man-made island – Hulhumale – and this has included an allowance for sea level rise.

In addition, declining pH and rising sea surface temperatures in the oceans will also adversely affect vulnerable marine ecosystems over the next few decades, although it is difficult to quantify these impacts. As well as intrinsic value, ecosystems are vital to humans in coastal areas to sustain lives and earn a living through activities such as fishing. Healthy ecosystems, such as coral reefs and mangroves, also provide a natural protection for the land behind them from storm surges and cyclone.

What can we do to avoid negative impacts?

Based on current levels of emissions, we are on course to exceed a 2˚C global average temperature increase. A reduction in emissions needs to happen urgently in order to meet the 1.5°C target. Given current trajectories, this reduction is highly ambitious and will require many transformational changes to the way we live – and political commitment. At the end of this year the United Nations Framework Convention on Climate Change will convene its 24thConference of the Parties in Katowice, Poland, where the findings of the IPCC SR will inform negotiations. Further climate stabilisation is often considered just to be for carbon dioxide, but it is required across all greenhouse gases (methane, ozone, nitrous oxides, etc).

For coasts and deltas, the imperative to act now is even greater because the real benefits of climate mitigation for sea level rise are over multi-centennial timescales. Sea levels continue to rise in a stable climate due to so-called ‘commitment to sea level rise’. Therefore we need some adaptation as well as reducing our greenhouse gas emissions to make sea level rise manageable and avoid the most negative impacts.

How can we adapt?

Adaptation can take many forms but, given that we know to expect these changes, the key is to plan now so that we are ready. We already have a variety of options at hand: hard engineering solutions such as dykes and embankments; planning regulations to avoid heavy investment in the most at risk areas; and soft adaptations that enable people to make a living from the changing conditions (for example switching to saline-tolerant crop varieties, or aquaculture instead of farming). Portfolios of adaptation options are likely to be most effective – ideally as sequenced actions known as adaptation pathways. The magnitude of change that we will see will require innovation, such as working with nature, or controlled flooding and sedimentation in deltas to raise land levels.

Are you optimistic?

At the current rate of emissions, we are on course to exceed 1.5°C between 2030 and 2052. That means that time really is running out for us to make the choices necessary to avoid negative impact of climate change on coasts and deltas. We have options to adapt to the sea level rise to which we are already committed. However, we will make it much easier for ourselves if we – individually, collectively and politically – can make the lifestyle changes required to keep temperature rise to 1.5˚C, and sea level rise to less than half a metre this century. This will not be easy – the Special Report says we will have to halve CO2 emissions within 11 years and go zero carbon by 2050. It is our hope that the evidence presented in the Special Report is a sufficient catalyst for this.


Global warming of 1.5°C English

Document links last validated on: 16 July 2021

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