Limiting global warming to 2℃ is not enough – why the world must keep temperature rise below 1℃

Warming of more than 1℃ risks unsafe and harmful outcomes for humanity.
Ink Drop/Shutterstock

The Paris Climate agreement represented a historic step towards a safer future for humanity on Earth when it was adopted in 2015. The agreement strove to keep global heating below 2℃ above pre-industrial levels with the aim of limiting the increase to 1.5℃ if possible. It was signed by 196 parties around the world, representing the overwhelming majority of humanity.

But in the intervening eight years, the Arctic region has experienced record-breaking temperatures, heatwaves have gripped many parts of Asia and Australia has faced unprecedented floods and wildfires. These events remind us of the dangers associated with climate breakdown. Our newly published research argues instead that humanity is only safe at 1℃ of global warming or below.

While one extreme event cannot be solely attributed to global heating, scientific studies have shown that such events are much more likely in a warmer world. Since the Paris agreement, our understanding of the impacts of global heating have also improved.

A fishing boat surrounded by icebergs that have come off a glacier.
Fishing boat dwarfed by icebergs that came off Greenland’s largest glacier, Jakobshavn Isbrae.
Jonathan Bamber, Author provided

Rising sea levels are an inevitable consequence of global warming. This is due to the combination of increased land ice melting and warmer oceans, which cause the volume of ocean water to increase. Recent research shows that in order to eliminate the human-induced component of sea-level rise, we need to return to temperatures last seen in the pre-industrial era (usually taken to be around 1850).

Perhaps more worrying are tipping points in the climate system that are effectively irreversible on human timescales if passed. Two of these tipping points relate to the melting of the Greenland and West Antarctic ice sheets. Together, these sheets contain enough ice to raise the global sea level by more than ten metres.

The temperature threshold for these ice sheets is uncertain, but we know that it lies close to 1.5℃ of global heating above pre-industrial era levels. There’s even evidence that suggests the threshold may already have been passed in one part of west Antarctica.

Critical boundaries

A temperature change of 1.5℃ might sound quite small. But it’s worth noting that the rise of modern civilisation and the agricultural revolution some 12,000 years ago took place during a period of exceptionally stable temperatures.

Our food production, global infrastructure and ecosystem services (the goods and services provided by ecosystems to humans) are all intimately tied to that stable climate. For example, historical evidence shows that a period called the little ice age (1400-1850), when glaciers grew extensively in the northern hemisphere and frost fairs were held annually on the River Thames, was caused by a much smaller temperature change of only about 0.3℃.

A sign marking the retreat of a glacier since 1908.
Jasper National Park, Canada. Glaciers used to grow extensively in the Northern Hemisphere.
Matty Symons/Shutterstock

A recent review of the current research in this area introduces a concept called “Earth system boundaries”, which defines various thresholds beyond which life on our planet would suffer substantial harm. To avoid passing multiple critical boundaries, the authors stress the need to limit temperature rise to 1℃ or less.

In our new research, we also argue that warming of more than 1℃ risks unsafe and harmful outcomes. This potentially includes sea level rise of multiple metres, more intense hurricanes and more frequent weather extremes.

More affordable renewable energy

Although we are already at 1.2℃ above pre-industrial temperatures, reducing global temperatures is not an impossible task. Our research presents a roadmap based on current technologies that can help us work towards achieving the 1℃ warming goal. We do not need to pull a technological “rabbit out of the hat”, but instead we need to invest and implement existing approaches, such as renewable energy, at scale.

Renewable energy sources have become increasingly affordable over time. Between 2010 and 2021, the cost of producing electricity from solar energy reduced by 88%, while wind power saw a reduction of 67% over the same period. The cost of power storage in batteries (for when the availability of wind and sunlight is low) has also decreased, by 70% between 2014 and 2020.

An aerial photograph of a photovoltaic power plant on a lush hillside.
A photovoltaic power plant in Yunnan, China.
Captain Wang/Shutterstock

The cost disparity between renewable energy and alternative sources like nuclear and fossil fuels is now huge – there is a three to four-fold difference.

In addition to being affordable, renewable energy sources are abundantly available and could swiftly meet society’s energy demands. Massive capacity expansions are also currently underway across the globe, which will only further bolster the renewable energy sector. Global solar energy manufacturing capacity, for example, is expected to double in 2023 and 2024.

Removing carbon dioxide from the atmosphere

Low-cost renewable energy will enable our energy systems to transition away from fossil fuels. But it also provides the means of directly removing CO₂ from the atmosphere at a large scale.

CO₂ removal is crucial for keeping warming to 1℃ or less, even though it requires a significant amount of energy. According to research, achieving a safe climate would require dedicating between 5% and 10% of total power generation demand to effective CO₂ removal. This represents a realistic and attainable policy option.

Various measures are used to remove CO₂ from the atmosphere. These include nature-based solutions like reforestation, as well as direct air carbon capture and storage. Trees absorb CO₂ from the atmosphere through photosynthesis and then lock it up for centuries.

A group of people planting a mangrove forest next to the sea.
A mangrove forest being planted in Klong Khone Samut Songkhram Province, Thailand.
vinai chunkhajorn/Shutterstock

Direct air capture technology was originally developed in the 1960s for air purification on submarines and spacecrafts. But it has since been further adapted for use on land. When combined with underground storage methods, such as the process of converting CO₂ into stone, this technology provides a safe and permanent method of removing CO₂ from the atmosphere.

Our paper demonstrates that the tools and technology exist to achieve a safer, healthier and more prosperous future – and that it’s economically viable to do so. What appears to be lacking is the societal will and, as a consequence, the political conviction and commitment to achieve it.



This blog is written Cabot Institute for the Environment member Jonathan Bamber, Professor of Glaciology and Earth Observation, University of Bristol and Christian Breyer, Professor of Solar Economy, Lappeenranta University of TechnologyThis article is republished from The Conversation under a Creative Commons license. Read the original article.

Jonathan Bamber
Jonathan Bamber

Why are neonicotinoids so polarised?

Bee on yellow flower

The use of neonicotinoid insecticides has been, and still is, a topic of huge controversy and dispute. To use an appropriate analogy, stakeholders appear to fall into one of two neighbouring fields, distinctly fenced off from one another.

In one field, there are those that believe that the scientific evidence revealing the impacts of neonicotinoid compounds on pollinators and the wider environment is more than sufficient to strictly ban their use as a pest management tool. In the other field, interested parties argue that the evidence is convoluted and context specific, and that in some circumstances neonicotinoid use can be a safe, and environmentally resourceful strategy.

But why has this topic become so polarised? And why is there increasingly less space for those that wish to ‘sit on the fence’? This blog summarises the research published in a recent paper by Hannah Romanowski and Lauren Blake. The paper investigates the causes of controversy, and analyses the viability of alternatives in the UK sugar beet system.

What are neonicotinoids?

Neonicotinoids (neonics) are a group of synthetic compounds used as the active ingredient in some insecticides. They are neuroactive, which means that they act on the nervous system of the insect, causing changes in behaviour. They specifically bind to receptors of the nicotinic acetylcholine (nAChRs) enzyme, which are specific to insects, meaning neonics have low toxicity to vertebrates, such as mammals. They are used to control a variety of pests, especially sap-feeding insects such as aphids. Neonics are a systemic pesticide, meaning that they are absorbed by the whole plant (either by seed coating or spraying) and distribute throughout all the plants tissue.

Are neonics legal in the UK?

That’s where things get confusing… the answer is both yes and no. In 2018, the UK prohibited the outdoor use of neonics following a review of the evidence about their risk to pollinators, published by the European Food Safety Authority. However, the UK and many other EU member states have since granted emergency authorisations, which allows the use of neonics under a set of specific circumstances and conditions. The best-known example of this in the UK is the emergency authorisations granted in 2021, 2022 and 2023 for the use of thiamethoxam, one of the banned neonicotinoid compounds, on sugar beet.

However, even if an emergency authorisation is approved by UK Government, the predicted virus incidence (forecasted by Rothamsted Insect Survey) in a given year must be above a decided threshold before authorisation is fully granted. If the threshold is not met, neonicotinoids use remains prohibited. In 2021 for example, Defra set the threshold at 9%, and since the forecast of the virus was only 8.37%, the neonicotinoid seed treatment was not used. The crop went on to grew successfully unscathed by the virus.

Why is sugar beet an exception?

The Expert Committee on Pesticides (ECP) produced a framework in 2020 that laid out a list of requirements for an emergency authorisation of a prohibited pesticide. Requirements include not having an alternative, adequate evidence of safety, limited scale and control of use, and evidence of a permanent solution in development. In essence, the long-term economic and environmental benefits of granting the temporary emergency authorisation must outweigh any potential adverse effects resulting from the authorisation.

Sugar beet farm in Switzerland
Sugar beet farm. Source: Volker Prasuhn, Wikimedia.

Sugar beet is extremely vulnerable to a yield-diminishing group of viruses known as yellows virus (YV). YV are transmitted by an aphid vector, Myzus persicae, which are effectively controlled by neonic seed treatment. Compared to other crop systems, sugar beet is also considered low risk and ‘safer’ as it does not flower before harvest and is therefore not as attractive to pollinator insects. As was found during the research of this paper, there are currently no alternatives as effective as neonics in this system, but long-term solutions are in development. Since sugar beet produces 60% of white sugar consumed in the UK, the economic and environmental impacts of yield loss (i.e. from sugar imports) would be serious. In 2021, the government felt that sugar beet sufficiently met the requirements outlined by the ECP, and emergency authorisation was granted.

What were the aims of this paper?

The main aim of this study was to identify the key issues associated with the debate surrounding the emergency authorisation of neonics on sugar beet, and evaluate and compare current policy with potential alternatives.

Most of the data for this study was collected through semi-structured interviews with nine respondents, each representing a key stakeholder in this discussion. Interviews took place in 2021, just after the announcement that neonics would not be authorised, despite granting the emergency authorisation, as the threshold was not met.

What did this research find?

The main take-home from this research was that uncertainty around the scientific evidence was not the biggest concern to respondents, as was predicted. Instead, respondents were alarmed at the level of polarisation of the narrative.  It was broadly felt that the neonicotinoid debate illustrates the wider issues around environment discussions, that are falsely perceived as a dichotomy, fuelled by media attention, and undermining of science.

The organisation of the sugar beet industry was also considered an issue. In east England, where sugar beet is grown, local growers supply only one buyer, British Sugar. This means that for British Sugar to meet demand they use a contractual system, whereby growers are contracted each year to meet a particular yield. This adds pressure to growers, and means that British Sugar controls the seed supply and therefore the treatment of seeds with synthetic pesticides. One respondent in the study said, “At one time you couldn’t order seed that wasn’t treated with neonicotinoid’.

The study also found that alternatives such as Integrated Pest Management (IPM) and Host Plant Resistance (HPR) were not yet effective in this system. There were 3 reasons why IPM fails. Firstly, sugar beet has a very low yield diminishing threshold for the virus, meaning that it does not take much infection to significantly effect yield. Secondly, the system is extremely specific, meaning that general IPM practices do not work and research on specific methods of IPM (such as natural predators of Myzus persicae) are limited. HPR is in development, and some new varieties of plant with host resistance have been produced, but the virus has multiple strains and no HPR varieties are resistant to all of them. Finally, there is no incentivisation for farmers to take up alternative practices. Due to the contract system, the risk to growers of sugar beet to try new pest management strategies is too high.

What is the latest in 2023?

In 2023, another emergency authorisation was granted, however the threshold set by Defra was increased to 63% virulence. In March, the Rothamsted Virus Yellows forecast predicted an incidence of 67.51%, and so the neonicotinoid seed treatment was used. With this authorisation there are still conditions that growers are required to meet to mitigate any risk to pollinators. This includes no flowering crops being grown for 32 months after neonic treated sugar beet has grown, using herbicides to reduce the number of flowering weeds that may attract pollinators to the field growing treated sugar beet, and compliance with stewardship schemes such as monitoring of neonicotinoid residues in the environment.


This blog is written by Hannah Romanowski, Biological Sciences, University of Bristol. The paper that this blog is based on can be found here:

Hannah Romanowski


Arctic Ocean could be ice-free in summer by 2030s, say scientists – this would have global, damaging and dangerous consequences

Ice in the Chukchi Sea, north of Alaska and Siberia.
NASA Goddard Space Flight Center

The Arctic Ocean could be ice-free in summer by the 2030s, even if we do a good job of reducing emissions between now and then. That’s the worrying conclusion of a new study in Nature Communications.

Predictions of an ice-free Arctic Ocean have a long and complicated history, and the 2030s is sooner than most scientists had thought possible (though it is later than some had wrongly forecast). What we know for sure is the disappearance of sea ice at the top of the world would not only be an emblematic sign of climate breakdown, but it would have global, damaging and dangerous consequences.

The Arctic has been experiencing climate heating faster than any other part of the planet. As it is at the frontline of climate change, the eyes of many scientists and local indigenous people have been on the sea ice that covers much of the Arctic Ocean in winter. This thin film of frozen seawater expands and contracts with the seasons, reaching a minimum area in September each year.

Animation of Arctic sea ice from space
Arctic sea ice grows until March and then shrinks until September.

The ice which remains at the end of summer is called multiyear sea ice and is considerably thicker than its seasonal counterpart. It acts as barrier to the transfer of both moisture and heat between the ocean and atmosphere. Over the past 40 years this multiyear sea ice has shrunk from around 7 million sq km to 4 million. That is a loss equivalent to roughly the size of India or 12 UKs. In other words, it’s a big signal, one of the most stark and dramatic signs of fundamental change to the climate system anywhere in the world.

As a consequence, there has been considerable effort invested in determining when the Arctic Ocean might first become ice-free in summer, sometimes called a “blue ocean event” and defined as when the sea ice area drops below 1 million sq kms. This threshold is used mainly because older, thicker ice along parts of Canada and northern Greenland is expected to remain long after the rest of the Arctic Ocean is ice-free. We can’t put an exact date on the last blue ocean event, but one in the near future would likely mean open water at the North Pole for the first time in thousands of years.

Annotated map of Arctic
The thickest ice (highlighted in pink) is likely to remain even if the North Pole is ice-free.
NERC Center for Polar Observation and Modelling, CC BY-SA

One problem with predicting when this might occur is that sea ice is notoriously difficult to model because it is influenced by both atmospheric and oceanic circulation as well as the flow of heat between these two parts of the climate system. That means that the climate models – powerful computer programs used to simulate the environment – need to get all of these components right to be able to accurately predict changes in sea ice extent.

Melting faster than models predicted

Back in the 2000s, an assessment of early generations of climate models found they generally underpredicted the loss of sea ice when compared to satellite data showing what actually happened. The models predicted a loss of about 2.5% per decade, while the observations were closer to 8%.

The next generation of models did better but were still not matching observations which, at that time were suggesting a blue ocean event would happen by mid-century. Indeed, the latest IPCC climate science report, published in 2021, reaches a similar conclusion about the timing of an ice-free Arctic Ocean.

As a consequence of the problems with the climate models, some scientists have attempted to extrapolate the observational record resulting in the controversial and, ultimately, incorrect assertion that this would happen during the mid 2010s. This did not help the credibility of the scientific community and its ability to make reliable projections.

Ice-free by 2030?

The scientists behind the latest study have taken a different approach by, in effect, calibrating the models with the observations and then using this calibrated solution to project sea ice decline. This makes a lot of sense, because it reduces the effect of small biases in the climate models that can in turn bias the sea ice projections. They call these “observationally constrained” projections and find that the Arctic could become ice-free in summer as early as 2030, even if we do a good job of reducing emissions between now and then.

Walruses on ice floe
Walruses depend on sea ice. As it melts, they’re being forced onto land.
outdoorsman / shutterstock

There is still plenty of uncertainty around the exact date – about 20 years or so – because of natural chaotic fluctuations in the climate system. But compared to previous research, the new study still brings forward the most likely timing of a blue ocean event by about a decade.

Why this matters

You might be asking the question: so what? Other than some polar bears not being able to hunt in the same way, why does it matter? Perhaps there are even benefits as the previous US secretary of state, Mike Pompeo, once declared – it means ships from Asia can potentially save around 3,000 miles of journey to European ports in summer at least.

But Arctic sea ice is an important component of the climate system. As it dramatically reduces the amount of sunlight absorbed by the ocean, removing this ice is predicted to further accelerate warming, through a process known as a positive feedback. This, in turn, will make the Greenland ice sheet melt faster, which is already a major contributor to sea level rise.

The loss of sea ice in summer would also mean changes in atmospheric circulation and storm tracks, and fundamental shifts in ocean biological activity. These are just some of the highly undesirable consequences and it is fair to say that the disadvantages will far outweigh the slender benefits.


This blog is written by Cabot Institute for the Environment member Jonathan Bamber, Professor of Physical Geography, University of Bristol. This article is republished from The Conversation under a Creative Commons license. Read the original article.

Jonathan Bamber
Jonathan Bamber

Why 40°C is bearable in a desert but lethal in the tropics

Phew: heat plus humidity can make Bangkok an uncomfortable place in a heatwave.
Pavel V.Khon/SHutterstock

This year, even before the northern hemisphere hot season began, temperature records were being shattered. Spain for instance saw temperatures in April (38.8°C) that would be out of the ordinary even at the peak of summer. South and south-east Asia in particular were hammered by a very persistent heatwave, and all-time record temperatures were experienced in countries such as Vietnam and Thailand (44°C and 45°C respectively). In Singapore, the more modest record was also broken, as temperatures hit 37°C. And in China, Shanghai just recorded its highest May temperature for over a century at 36.7°C.

We know that climate change makes these temperatures more likely, but also that heatwaves of similar magnitudes can have very different impacts depending on factors like humidity or how prepared an area is for extreme heat. So, how does a humid country like Vietnam cope with a 44°C heatwave, and how does it compare with dry heat, or a less hot heatwave in even-more-humid Singapore?

Weather and physiology

The recent heatwave in south-east Asia may well be remembered for its level of heat-induced stress on the body. Heat stress is mostly caused by temperature, but other weather-related factors such as humidity, radiation and wind are also important.

Our bodies gain heat from the air around us, from the sun, or from our own internal processes such as digestion and exercise. In response to this, our bodies must lose some heat. Some of this we lose directly to the air around us and some through breathing. But most heat is lost through sweating, as when the sweat on the surface of our skin evaporates it takes in energy from our skin and the air around us in the form of latent heat.

annotated diagram of person
How humans heat up and cool down.
Take from Buzan and Huber (2020) Annual Review of Earth and Planetary Sciences, Author provided

Meteorological factors affect all this. For example, being deprived of shade exposes the body to heat from direct sunlight, while higher humidity means that the rate of evaporation from our skin will decrease.

It’s this humidity that meant the recent heatwave in south-east Asia was so dangerous, as it’s already an extremely humid part of the world.

The limit of heat stress

Underlying health conditions and other personal circumstances can lead to some people being more vulnerable to heat stress. Yet heat stress can reach a limit above which all humans, even those who are not obviously vulnerable to heat risk – that is, people who are fit, healthy and well acclimatised – simply cannot survive even at a moderate level of exertion.

One way to assess heat stress is the so-called Wet Bulb Globe Temperature. In full sun conditions, that is approximately equivalent to 39°C in temperature combined with 50% relative humidity. This limit will likely have been exceeded in some places in the recent heatwave across south-east Asia.

In less humid places far from the tropics, the humidity and thus the wet bulb temperature and danger will be much lower. Spain’s heatwave in April with maximum temperatures of 38.8°C had WBGT values of “only” around 30°C, the 2022 heatwave in the UK, when temperatures exceeded 40°C, had a humidity of less than 20% and WBGT values of around 32°C.

Two of us (Eunice and Dann) were part of a team who recently used climate data to map heat stress around the world. The research highlighted regions most at risk of exceeding these thresholds, with literal hotspots including India and Pakistan, south-east Asia, the Arabian peninsula, equatorial Africa, equatorial South America and Australia. In these regions, heat stress thresholds are exceeded with increased frequency with greater global warming.

In reality, most people are already vulnerable well below the survivability thresholds, which is why we can see large death tolls in significantly cooler heat waves. Furthermore, these global analyses often do not capture some very localised extremes caused by microclimate processes. For example a certain neighbourhood in a city might trap heat more efficiently than its surroundings, or might be ventilated by a cool sea breeze, or be in the “rain shadow” of a local hill, making it less humid.

Variability and acclimatisation

The tropics typically have less variable temperatures. For example, Singapore sits almost on the equator and its daily maximum is about 32°C year round, while a typical maximum in London in mid summer is just 24°C. Yet London has a higher record temperature (40°C vs 37°C in Singapore).

Given that regions such as south-east Asia consistently have high heat stress already, perhaps that suggests that people will be well acclimatised to deal with heat. Initial reporting suggests the intense heat stress of the recent heatwave lead to surprisingly few direct deaths – but accurate reporting of deaths from indirect causes is not yet available.

On the other hand, due to the relative stability in year-round warmth, perhaps there is less preparedness for the large swings in temperature associated with the recent heatwave. Given that it is not unreasonable, even in the absence of climate change, that natural weather variability can produce significant heatwaves that break local records by several degrees Celsius, even nearing a physiological limit might be a very risky line to tread.



This blog is written by Cabot Institute for the Environment members: Dr Alan Thomas Kennedy-Asser, Research Associate in Climate Science; Professor Dann Mitchell, Professor of Climate Science, and Dr Eunice Lo, Research Fellow in Climate Change and Health, University of Bristol. This article is republished from The Conversation under a Creative Commons license. Read the original article.

Alan Kennedy-Asser
Alan Kennedy-Asser
Dann Mitchell
Dann Mitchell
Eunice Lo
Eunice Lo