1.5 C vs 2 C global warming: New study shows why half a degree matters

1.5 C vs 2 C global warming: New study shows why half a degree matters
This image shows evidence of coral bleaching around Tioman Island, Malaysia. The warming difference between 1.5°C and 2°C could be decisive for the future survival of tropical coral reefs. Credit: Paul via Flickr

European researchers have found substantially different climate change impacts for a global warming of 1.5°C and 2°C by 2100, the two temperature limits included in the Paris climate agreement. The additional 0.5°C would mean a 10-cm-higher global sea-level rise by 2100, longer heat waves, and would result in virtually all tropical coral reefs being at risk. The research is published today (21 April) in Earth System Dynamics, an open access journal of the European Geosciences Union, and is presented at the EGU General Assembly.

"We found significant differences for all the impacts we considered," says the study's lead author Carl Schleussner, a scientific advisor at Climate Analytics in Germany. "We analysed the used in the [Intergovernmental Panel on Climate Change (IPCC)] Fifth Assessment Report, focusing on the projected impacts at 1.5°C and 2°C warming at the regional level. We considered 11 different indicators including extreme weather events, water availability, crop yields, and sea-level rise."

The team, with researchers from Germany, Switzerland, Austria and the Netherlands, identified a number of hotspots around the globe where projected at 2°C are significantly more severe than at 1.5°C. One of these is the Mediterranean region, which is already suffering from -induced drying. With a global temperature increase of 1.5°C, the availability of fresh water in the region would be about 10% lower than in the late 20th century. In a 2°C world, the researchers project this reduction to double to about 20%.

In tropical regions, the half-a-degree difference in global temperature could have detrimental consequences for crop yields, particularly in Central America and West Africa. On average, local tropical maize and wheat yields would reduce twice as much at 2°C compared to a 1.5°C temperature increase.

Tropical regions would bear the brunt of the impacts of an additional 0.5°C of global warming by the end of the century, with warm spells lasting up to 50% longer in a 2°C world than at 1.5°C. "For heat-related extremes, the additional 0.5°C increase marks the difference between events at the upper limit of present-day natural variability and a new climate regime, particularly in tropical regions," explains Schleussner.

The additional warming would also affect . Limiting warming to 1.5°C would provide a window of opportunity for some tropical coral reefs to adapt to climate change. In contrast, a 2°C temperature increase by 2100 would put virtually all of these ecosystems at risk of severe degradation due to coral bleaching.

On a global scale, the researchers anticipate sea level to rise about 50 cm by 2100 in a 2°C warmer world, 10 cm more than for 1.5°C warming. "Sea level rise will slow down during the 21st century only under a 1.5°C scenario," explains Schleussner.

Co-author Jacob Schewe, of the Potsdam Institute for Climate Impact Research in Germany, says: "Some researchers have argued that there is little difference in between 1.5°C and 2°C. Indeed, it is necessary to account for natural variability, model uncertainties, and other factors that can obscure the picture. We did that in our study, and by focusing on key indicators at the regional level, we clearly show that there are significant differences in impacts between 1.5°C and 2°C."

William Hare, a senior scientist and CEO at Climate Analytics who also took part in the Earth System Dynamics research, adds: "Our study shows that tropical regions - mostly developing countries that are already highly vulnerable to climate change - face the biggest rise in impacts between 1.5°C and 2°C."

"Our results add to a growing body of evidence showing that climate risks occur at lower levels than previously thought. It provides scientific evidence to support the call by vulnerable countries, such as the Least Developed Countries and Small Island Developing States, that a 1.5°C warming limit would substantially reduce the impacts of change," says Hare.


Explore further

UN climate panel to explore 1.5-degree warming goal

More information: Carl-Friedrich Schleussner et al. Differential climate impacts for policy-relevant limits to global warming: the case of 1.5 °C and 2 °C, Earth System Dynamics (2016). DOI: 10.5194/esd-7-327-2016
Citation: 1.5 C vs 2 C global warming: New study shows why half a degree matters (2016, April 21) retrieved 16 June 2019 from https://phys.org/news/2016-04-global-degree.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
37 shares

Feedback to editors

User comments

Apr 21, 2016
I have about as much faith in these predictions as I do in the ability of global climate computer models to predict what the temperature will be due to increasing carbon emissions.

I do have faith in the politicians who want more control over energy use to continue funding these kind of studies, along with my faith in the "scientists" who want to continue receiving these funds for writing these reports.

Apr 21, 2016
As ForFreeMinds says, the global climate models are not very good predictive tools. The most recent report, AR5 (2013), from the Intergovernmental Panel on Climate Change (IPCC) shows the difference between the GCM projections and measured temperatures is growing. All the GCM projections overstate warming. Have a look yourself:

https://www.ipcc....S-14.jpg

If a model doesn't accurately portray what's really going on, the model is incorrect. That's science.

If a flawed model portrays a scenario that a lot of people believe--and even hope--to be true it will still be used to make predictions. That's politics.


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more