Scientists describe the world after 1.5 degrees of global warming and ask people and governments to make some decisions.

A new report from the Intergovernmental Panel on Climate Change (IPCC) warns of the consequences of allowing global warming to reach 1.5°C above pre-industrial levels.

Half a degree matters: half a degree of warming can make a world of difference for certain impacts Dr Joeri Rogelj Report co-author and Grantham Lecturer

In their most authoritative assessment yet, the report by the United Nations scientist used data from 6000 independent studies to predict severe effects on sea level rise, increased heatwaves, lost coral reefs and depleted crop yields, all of which become more severe if global warming rises to 2°C.

Imperial College London experts were involved in the preparation of the report, with Dr Joeri Rogelj, Grantham Institute's Lecturer in Climate Change and the Environment coordinating and leading a chapter on climate change and sustainable development, and Professor Jim Skea from the Centre for Environmental Policy as co-chair of Working Group III, with responsibility for the report and its dissemination.

"Half a degree matters: half a degree of warming can make a world of difference for certain impacts," said Dr Rogelj. "Ways of keeping warming close to 1.5°C relative to preindustrial levels have been identified, and they all highlight the need for urgency."

The scientists recommended that in order to have a good chance of limiting the temperature rise to 1.5°C, human activities across the globe should be carbon-neutral by 2047. The urged measures to create smart cities with low-energy and few waste resources, alongside technological advances in agriculture, transport, manufacturing, homes and living.

"Deeper emissions reductions are required over the next decade to keep the window for limiting warming to 1.5°C open," said Dr Rogelj. Many scientists agree it will be necessary to call on unproven and expensive technologies to remove greenhouse gases, like carbon dioxide, from the atmosphere in order to reverse the warming effect.

It is hoped the findings presented in the IPCC Special Report on 1.5°C will guide national and international policymakers to strengthen the global response to the threat of climate change, whilst ensuring that all people around the world get access to opportunities for improved health and prosperity.

Read the report at the IPCC website. Experts from Imperial College London and the Grantham Institute - Climate Change and the Environment give their comments below.

Professor Joanna Haigh, co-director of the Grantham Institute – Climate Change and the Environment:

"It was a huge and significant achievement to reach a unanimous agreement at the 2015 UN climate conference in Paris, that all parties would work together to limit global warming since the mid-nineteenth century to well below 2°C and preferably to 1.5°C. At that time, however, it was not clear how the impacts of these two thresholds would differ.

"Today’s report lays out the potential advantages of constraining global temperature rise to 1.5°C compared with the 2°C. Some of these are dramatic; for example, coastal flooding affecting 10 million fewer people across the world and 50% fewer people experiencing water scarcity.

"The report says that to meet the 1.5°C target, emissions need to be cut by about 45% by 2030. It also concludes that it will probably be necessary to implement schemes for the extraction of carbon dioxide from the air.

"Without concerted and swift international action to reduce emissions of greenhouse gases, the 1.5°C threshold is likely to be passed by 2040 and the report sets out very starkly the costs of inaction. It also shows the substantial co-benefits, in terms of employment, health, economy and political stability, which can arise from decarbonisation.

"I hope this report will be used to drive international ambitions to drive down carbon emissions and it behoves all of us to consider changes to the way we live."

Dr Ajay Gambhir, Senior Climate Change Mitigation Policy Research Fellow:

"I've seen other IPCC assessment report launches but this one feels different. It feels like this is our last chance to take decisive action at reasonable economic costs to avoid dangerous climate change. As the evidence in the report lays out, there is so much to be gained from doing so. We would be collectively very foolish not to act now."

Dr Heather Graven, Senior Lecturer in the Department of Physics:

"Meeting a 1.5°C target requires a huge step up in global actions to reduce greenhouse gas emissions. Measurements show that atmospheric CO₂ concentration is increasing faster than ever, indicating very little progress towards the 1.5°C ambition in the three years since the Paris Agreement. It is imperative we continue, and expand, our monitoring efforts to observe the changes occurring in the atmosphere and to attribute changes in greenhouse gas concentrations to emissions from particular regions and activities."

Mr Neil Hirst, Senior Policy Research Fellow and author of The Energy Conundrum, Climate Change, Global Prosperity, and the Tough Decisions We Have to Make.

"This stark new report comes as the International Energy Agency reveals that world emissions are still rising. We are on a dangerous path and there is a harsh contrast between environmental necessity and today’s reality. We need a powerful response at the level of global energy policy."

Dr Ana Mijic, Senior Lecturer in the Department of Civil and Environmental Engineering:

"Limiting warming to 1.5°C presents an immersive challenge for society as a whole, but equally it opens a new set of opportunities to move towards collective, responsible decisions. For my area of water security and environmental management, this means bringing together policymakers, industry leaders, citizens and researchers in a joint effort to understand implications of our individual decisions. This includes large scale carbon-intensive infrastructure solutions and the role of water savings, efficiency, improved system control, nature-based solutions and water use behaviour to reduce the pressures on the fragile natural system."

Dr Tamaryn Napp, Grantham Institute Research Fellow:

"This new report lays out both the advantages and challenges of limiting global temperature rise to 1.5°C compared to 2°C or above. It will be expensive, but it is worth it to avoid the devastating climate-related impacts. Limiting global temperature rise to 1.5°C will require a complete transformation of the way we supply and consume energy across all sectors of the economy. Reduction of carbon dioxide emissions must begin immediately and be sustained over the coming decades. Energy systems models show very clearly that there is no single technology or sector that can address the problem. This means that everyone needs to do their bit. Individuals, businesses, governments and nations need to work together towards this common goal."

Professor Martin Siegert, co-director of the Grantham Institute – Climate Change and the Environment:

"The IPCC report states that we must reduce our carbon emissions by 40% of today's value by 2030 - that's just 12 years' time. There is no silver bullet for this. We each need to take action now, individually and collectively else we will run past 1.5°C in around 20 years' time. If governments, cities and businesses do not already describe how to accommodate the necessary reduction in greenhouse gas emissions in their five to ten year strategic plans, they must be immediately revisited and reworked."

Professor Richard Templer, Director of Innovation at the Grantham Institute:

"The IPCC's report tells us that innovation is required in all areas of human activity that cause greenhouse gas emissions. We have made progress on decarbonising electricity but that leaves a huge territory still to be touched. Agriculture, steel and cement productions are all major emitters for which we have yet to see major inroads.

"More importantly it is now absolutely obvious that we need technologies to remove carbon dioxide from the atmosphere. We need to get started now if we are to avoid warming of 2°C."