The Emergency on Planet Earth provides an easy-to-understand guide to the science of climate change. (You can also access it in a PDF format)

Published in September 2020, the document covers the science of both the climate and ecological emergencies in a clear and comprehensive way, no matter your level of scientific experience. It was written by Dr Emily Grossman with the support of the Scientists for XR community. It has been rigorously fact-checked, referenced and reviewed by a wide range of experts, and has been endorsed by some of the leading voices in the field.

“A fantastic communication summary of the science of climate/ecological crises. This document represents more than a year of careful work by one of the UK’s most talented and dedicated science communicators, with the support of some of its most eminent climate scientists. It should be of immense help to journalists, educators and anyone who cares about human life on earth, but often has difficulty navigating the scientific knowledge. This is an immense step forward in creating an educated public on climate topics.”
Professor Julia Steinberger, Professor of Social Ecology and Ecological Economics at the University of Lausanne and Lead Author of Working Group 3 of the IPCC 6th Assessment Report

Humanity is facing a crisis unprecedented in its history. A crisis that, unless immediately addressed, threatens to catapult us further into the destruction of all we hold dear: this nation, its peoples, our ecosystems and the future of generations to come. 

The science is clear: the world is warming and the breakdown of our climate has begun. There will be more wildfires, unpredictable super storms, scorching heat waves, rising sea levels and droughts. Vast tracts of land could be rendered uninhabitable through flooding and desertification. Our food supplies and fresh water are at risk of being cut off. Mass migration and famine could take us towards civil unrest, societal collapse, and ultimately war.

But that’s not all.

Around the world, biodiversity is being annihilated at a terrifying rate. We are entering the ‘sixth mass extinction’ event - with one million species at threat of extinction over the next few decades due to human intervention - and the consequences could be catastrophic if we do not act swiftly. Millions of trees are being felled to make room for our ever-increasing demands for palm oil, clothes and meat. We are running out of raw materials and using up our resources. Our rivers are being poisoned and our seas are acidifying and full of plastic. The air is so toxic that the UK is breaking the law: harming the unborn whilst causing tens of thousands to die. 

As Sir David Attenborough put it: “We are facing a man-made disaster on a global scale.”

These climate and ecological crises can no longer be ignored or denied. In spite of promises from governments, greenhouse gas emissions continue to rise steeply and biodiversity loss shows no sign of slowing. The time has come to take radical action. The future of our planet is at stake. 

1.  How do we know that the Earth is warming?

Independent temperature records from multiple official sources confirm that there is absolutely absolutely no doubt whatsoever that the Earth is warming. 

Indeed, each of the last three decades has been successively warmer than the one before, 19 of the top 20 warmest years have occurred in the last 19 years, and the past four years have been the hottest on record.  2016 was the hottest year ever recorded, whilst in 2019, nearly 400 temperature records were broken across 29 countries, June 2019 was the hottest on record, and July 2019 was the hottest month ever recorded. As of July 2020, January 2020 was the warmest January ever recorded in Europe, we saw the hottest May ever and we already have an 85% chance that 2020 will turn out to be the hottest year on record. 

2. Hasn’t it been hotter than this in the past?

The planet is now very probably hotter than at any point in at least the last 125,000 years, long before human civilisation began, when sea levels reached over 6 m higher than they are today.

But what’s even more concerning is how fast our temperatures are rising. Over the past 45 years, our planet’s temperature has been increasing a whopping 170 times faster than the baseline rate of cooling over the previous 7,000 years. Indeed, our current rate of warming is unprecedented over the last 10,000 years. 

Over the rest of this century, future temperature rises are predicted to be taking place not just much faster than it did during our recovery from the last ice age but hundreds of times faster than any extended period of warming in the last 65 million years. That’s when the dinosaurs went extinct. Crucially, when temperatures rise this fast, it is impossible for many living creatures and plants to have time to adapt to such changes. Not to mention the fact that many places on Earth that creatures would have previously used to take refuge from increasing temperatures have now been degraded, fragmented or colonised by human activities.

The bottom line is that the changes in temperatures that we’ve been seeing on our planet in recent years are truly unprecedented. 

3. Why is the Earth getting warmer?

The temperature at the Earth’s surface is controlled primarily by the levels of certain gases in the atmosphere, such as water vapour, carbon dioxide and methane. Although these gases only make up a tiny fraction of our atmosphere (current carbon dioxide levels are around 410 parts per million (ppm), which is just 0.041%), just like how a drop of ink can affect the colour of a huge volume of water, tiny amounts of these gases can have enormous impacts on our atmosphere. Due to their special structure, these molecules can absorb heat emitted from the Earth’s surface as a result of it having been warmed by the Sun, preventing some of that heat from escaping back out into Space. In this way, it can be said that the gases provide an insulating ‘blanket’ around the Earth, which traps heat in our atmosphere keeping us warm. 

4. What is the greenhouse effect?

This heating effect has (somewhat wrongly) been compared to how the glass roof of a greenhouse traps heat energy from the Sun, keeping the inside of the greenhouse warmer than its surroundings. Hence this phenomenon has become known as the greenhouse effect and the gases known as greenhouse gases. We have known about the greenhouse effect for well over 150 years, and the science behind it is well established. 

The greenhouse effect, in its natural form, is essential for life here on Earth; without greenhouse gases in our atmosphere, the average temperature at the Earth’s surface would be around -18°C, dropping to temperatures at night that would be far too cold for us to survive. However, by burning fossil fuels (as well as by farming cattle, growing rice, burning trees, intensively ploughing soil and using chemical fertilisers) humans have been adding huge quantities of additional greenhouse gases into the atmosphere, ‘supercharging’ the greenhouse effect beyond anything that humans have ever experienced.

5. Doesn’t the Earth’s climate change naturally?

Analysis of air bubbles trapped in Antarctic ice sheets reveals that over the past 800,000 years there also have been periods in the Earth’s history where the carbon dioxide levels have naturally risen and fallen, however this has taken place extremely gradually. These changes are brought about by natural variations in the way in which the Earth travels around the Sun (known as Milankovitch cycles), which lead to changes in the absorption of sunlight on Earth. For example, a small increase in the amount of sunlight being absorbed causes the oceans to warm slightly, which results in some of the carbon dioxide dissolved within them being released back into the atmosphere. The increase in atmospheric carbon dioxide leads to more ocean warming, which causes more carbon dioxide to be released, which causes more warming... and so on and so forth. The changes in temperature caused by this feedback loop, and others like it, drive the transitions into ice ages and back out of them. The last time this happened was around 17,000 years ago, when we began to transition out of our most recent ice age. 

The key point here is that these natural changes in carbon dioxide levels, triggered by cycles in the Earth’s orbit and modulated by feedback cycles, take place over tens of thousands of years. In contrast, the extremely rapid increases in carbon dioxide levels that we have been seeing over the past 60 years, due to human actions, have been taking place about 100 times faster than any of these previous natural increases.  

6. Is the rise in carbon dioxide levels due to human activity?

Since the Industrial Revolution, humans have been pumping enormous additional quantities of carbon dioxide into the atmosphere due to the burning of fossil fuels: coal, oil and natural gas. Fossil fuels are naturally occurring substances that were formed millions of years ago from the remains of dead plants and sea-creatures. When these fuels are burnt, the carbon compounds that have remained trapped underground for millions of years are converted into carbon dioxide and released, adding extra carbon dioxide into the atmosphere that would not naturally be there. 

In addition, deforestation on massive scales to clear land for agriculture and livestock has released huge amounts of carbon dioxide back into the atmosphere, and has also meant that there are increasingly fewer trees to absorb excess carbon dioxide from the air. At the same time as humans have been burning fossil fuels and clearing forests, they have also been churning up our planet’s soils through intensive farming practices. Healthy soils hold around 70% of the planet’s land-based organic carbon. However, when soil is repeatedly ploughed or compacted by heavy machinery or livestock, its ability to store carbon is compromised and vast quantities are released back into the atmosphere in the form of carbon dioxide.

It’s not just carbon dioxide levels that are increasing due to human actions. Methane levels have more than doubled in the last 150 years. Leaks from the oil and gas industry contribute heavily to the amount of methane in our atmosphere, but the waste sector and agriculture are also major sources. There has also been a huge increase in the number of rice-producing paddy fields and in the breeding of cattle for the meat and dairy industries. Microbes in the waterlogged soils of flooded rice fields release large quantities of methane, as do cows and sheep when they burp and fart due to the presence of similar kinds of microbes in their stomachs that help them to digest grass. In addition, fertilisers and animal waste produce large quantities of nitrous oxide, increasing its levels by around a third in the past 150 years.

As our greenhouse gas emissions have risen, so too have global temperatures. 

7. Can we be sure that human activity is causing global heating?

Yes, we can. 

There is now absolutely no doubt that the recent increase in global temperatures is almost entirely due to human factors. A vast body of peer-reviewed scientific evidence confirms that natural cycles, volcanic activity, galactic cosmic rays and changes in solar activity from sunspots have had a negligible effect on our current temperature rise. Instead, rises in global temperature have followed the trajectory of increased greenhouse gas levels.

Indeed, scientists have been able to find an unmistakable “human fingerprint” on climate change. Firstly, the Earth’s atmosphere is reacting exactly as we would expect it to if it were being exposed to an increase in greenhouse gases (as opposed to, for example, if it were experiencing increased solar activity). Secondly, detailed analysis of the carbon atoms in the carbon dioxide accumulating in the atmosphere shows that they must have been released by the burning of fossil fuels. Thirdly, measurements taken by satellites show that increases in greenhouse gases are trapping infra-red radiation from the Earth and causing the atmosphere to heat up.

Whilst climate change deniers sometimes post articles or comments from scientists that seem to refute the overwhelming evidence of human-caused global heating, these articles often rely on inaccurate claims about climate science. The scientists themselves tend not to have expertise in a climate-related field, or they have links to the fossil fuels industry - or both. 

The scientific community as a whole are overwhelmingly concerned about what is going on on our planet. In the words of Professor Lonnie Thompson, director of the Byrd Polar Research Centre: “Virtually all of us are now convinced that global warming poses a clear and present danger to civilization.”

Or as the Intergovernmental Panel on Climate Change said in their last assessment report:

“Evidence for man-made warming of our climate system is unequivocal.” 

8. Aren’t governments trying to bring greenhouse gas emissions down?

Nowhere near enough. In a word, no. 

In 2016 the Paris Agreement was drawn up by negotiators from almost every country in the world as part of the United Nations Framework Convention on Climate Change. The Agreement commits governments “to strengthen the global response to the threat of climate change by keeping a global temperature rise this century well below 2°C above pre-industrial levels and to pursue efforts to limit the temperature increase even further to 1.5°C.” A total of 189 countries have given their formal consent to the agreement, as well as the European Union. 

In order to reach this target, there is a finite amount of carbon dioxide that can still be emitted, known as the carbon budget. The recent IPCC report found that in order to have a 50% chance of remaining below a 1.5 warming, global carbon dioxide emissions need to halve by 2030, and get to net zero by 2050. For a 66% chance of staying below 1.5C, we have a 420Gt global carbon budget. 

Not only are governments not doing everything in their power to bring global greenhouse gas emissions down in line with the Paris Agreement, they are supporting further increases in emissions.

Whilst it is true that some climate policies have indeed been implemented over the past few years and it is therefore hoped that the absolute worst-case scenarios are now less likely, according to the latest UN Emissions Gap Report the government policies in place right now are so woefully inadequate that they do not leave us in a much better position than if we had no policies in place at all. Global carbon emissions continue to shoot up and the situation is getting worse not better. 

It’s important to note here that whilst there has been a recent drop in emissions due to the COVID-19 pandemic, the short term effects on climate will be minimal and unless concerted effort is taken to stop fossil fuel development in the recovery period it will only be a temporary dip in a long-term upward trend.

Professor Stephan Harrison, Professor of Climate and Environmental Change, University of Exeter, UK said in a recent lecture: 

"We have all the resources we need to deal with this. There is nothing magical about reducing carbon dioxide in the atmosphere. There is nothing magical about the greenhouse effect. We know exactly how to deal with it. We just don’t have the political or economic will to do this.”

9. What is global heating doing to our weather?

Global heating is having a huge impact on our natural weather systems. This is because the increased amount of heat energy trapped in the Earth’s atmosphere and oceans (as a result of greenhouse gas emissions) increases the total amount of energy in our weather systems. As a result, global heating doesn't just cause an overall rise in global temperatures, it also leads to more frequent and more extreme heatwaves, heavier rainfall, and more intense tropical storms and hurricanes. Generally, wetter areas are getting wetter, increasing the risk of flooding, and dryer areas are getting drier, increasing the risk of droughts and forest fires.

The number of extreme climate-related disasters - including extreme heat, droughts, floods and storms - has doubled since the early 1990s and studies have shown that more than two thirds of all extreme weather events investigated were made more likely, or more severe, by human-caused climate change.

10. Is global heating causing the oceans to rise? 

As atmospheric conditions get hotter, the water in our oceans heats up too. Indeed, over 90% of the increased heat trapped in our atmosphere is being stored in the oceans. In 2019, the heat in the world’s oceans reached a new record level, confirming “irrefutable and accelerating” heating of the planet. It has been calculated that the heat energy being absorbed by the oceans is the equivalent of between 3 to 6 Hiroshima-size atomic bombs every second. 

All this this extra heat causes the water to expand and take up more space, resulting in rises in sea levels. 

In addition, hotter water in our oceans, along with hotter air in our atmosphere, leads to the melting of sea ice, ice sheets and mountain glaciers. Fortunately, when sea ice melts it doesn’t affect sea levels - just like how an ice cube melting in a glass of water doesn’t cause the water level to go up. However, when land-based ice sheets and glaciers melt, the water runs off into the sea, causing sea levels to rise - just like what would happen if you added another ice cube to the glass of water and waited for it to melt.

The Greenland ice sheet, the second largest in the world, is losing ice seven times faster than in the 1990s, whilst the Antarctic ice sheet has lost three trillion tonnes of ice in the past 25 years and is now losing 252 billion tonnes a year - that’s six times more than it was 30 years ago. 

Overall, over the past 40 years the amount of ice we have lost from our planet averages out to the loss of around 300 double-decker-sized chunks of ice... EVERY SECOND. 

Rising seas are already displacing hundreds of thousands of people from vulnerable coastal areas in the South Pacific, Indonesia and Bangladesh, and climate displacement is already well underway in places such as Vietnam. Over the past six decades, much of the Isle de Jean Charles, Louisiana - once home to 400 people - has disappeared due to subsidence caused by oil and gas extraction and now rising sea levels. In November 2019 it was reported that five whole Pacific Islands - part of the Solomon Islands - have now been entirely lost to rising sea levels, with a further six having large parts of their coastline eroded, destroying entire villages.

11. What are we doing to our land?

75% of the Earth’s land has now been severely altered by human actions such as industry and farming. Only 13% of the world’s oceans remain as wilderness, free from human influence and exploitation. Today, approximately 60 billion tonnes of renewable and nonrenewable resources are extracted globally each year from our ecosystems, nearly twice the figure from 1980. According to some studies we are producing wastes and using the Earth’s resources 70% more quickly than they can be absorbed or replenished, effectively using up our annual ecological budget by August each year. 

Since the onset of agriculture about 12,000 years ago, the number of trees worldwide has dropped by 46% - that’s the loss of a staggering 3 trillion trees. Forest cover is now at only 68% of what it was in preindustrial times, and around 15 billion trees are now being cut down each year. In the temperate zone, we retain only 1-2% of the original forest cover. The majority of tropical deforestation is driven by our demand for just four commodities - beef, soy, palm oil, and wood products. Palm oil is found in a myriad of popular products such as soaps, shampoo, chocolate, bread and even crisps.

Intensive agriculture is by far the biggest driver of global deforestation and wildlife loss and is severely damaging our soils and waters. Currently a massive 26% of the planet's ice-free land is used for livestock grazing, with an area the size of Panama (18 million acres) being lost to livestock production each year.

Increased deforestation, overgrazing and the use of chemicals are also causing severe damage to our soils. This process is exacerbated by increases in extreme weather events, such as extreme rainfall that causes fertile topsoil to be washed away into rivers, or increased erosion due to drought, winds, or high temperatures. A whopping 95% of what we eat relies on healthy soils, so degradation of our soils is having a huge impact on global food production.

12. What are we doing to the air we breathe?

According to the World Health Organisation, a staggering 9 out of 10 people on our planet breathe polluted air (that’s air containing high levels of pollutants), with most air pollutants that we are exposed to coming from the burning of fossil fuels. Indeed, air pollution is the world’s largest environmental cause of disease and premature death across the globe, being responsible for an estimated 7 million premature deaths each year, with 4.8 million dying from outdoor pollution, and the remainder from household pollution. Overall, air pollution kills more people each year than smoking.

The sources of air pollution vary across the world. In many places traffic emissions are now the major source of air pollution but other important sources include industry, coal-fired power plants, agriculture and households. People are also exposed to air pollution in their own homes through indoor burning of fossil fuels and biomass-based fuels such as wood for cooking, lighting and heating. Wildfires also dramatically worsen air pollution in broad areas. 

As Professor Thomas Munzel, Specialist in Interventional Cardiology, Risk Factors and Prevention, University Medical Centre of Mainz says;

“There is an air pollution pandemic” 

13. How are we polluting our waters?

We are also severely polluting our waters. Since 1980, there has been a ten-fold increase in plastic pollution, with now an estimated 300 kg of plastic entering the ocean every second. This adds up to a staggering 4.8-12.7 million metric tonnes of consumer plastics ending up in the world’s oceans each year. Plastic pollution has resulted in the presence of more than 100 million particles of macroplastics in only 12 regional seas worldwide, and 51 trillion particles of microplastic floating on the ocean surface globally.  A recent study found that off the coast of Oregon, USA, there’s an average of 11 tiny pieces of plastic to every oyster. Nearly all of these microplastic pieces came from clothing fibres or abandoned fishing gear.

Unfortunately, recycling isn’t necessarily the answer to this problem. Shockingly, a huge proportion of ‘recycled’ plastic actually ends up in the ocean, buried in landfill or even being burned. Due to ocean currents, there are now areas in the ocean where enormous amounts of plastic collects in one place, resulting in huge ‘garbage dumps of the sea’. The Great Pacific Garbage Patch for example, which is halfway between Hawaii and California, contains more than 1.8 trillion pieces of plastic, weighs more than 43,000 cars and is three times the size of France.

Plastics are not the only pollutant in our seas and freshwaters. Pesticides, herbicides, detergents, industrial chemicals, oil and sewage also make their way into our waters, as well as soil eroded from the land by human activities. More than 80% of wastewater resulting from human activities is discharged into rivers or sea without any pollution removal. Nitrates from the use of agricultural fertilisers are now the most common chemical contaminant in our groundwater. Indeed, human activity now produces as much nitrogen on an annual basis as all the world's natural processes combined. These nitrates can find their way into lakes and coastal waters, and along with phosphates, cause algal blooms which poison waters and dramatically reduce the growth of plants and fish through a process called eutrophication. In addition, 300-400 million tonnes of poisonous heavy metals, solvents, toxic sludge, and other wastes from industrial facilities are dumped annually into the world’s waters.

14. Why should we care about the loss of our wildlife?

Not only do our fellow species have as much a right to exist as we do, nature also supports human life here on Earth in a multitude of ways. Insects pollinate our crops, and a range of animals eat the pests that would otherwise destroy the crops on which we rely. Animals, microbes and fungi decompose and recycle dead matter, enriching our soils and recycling nutrients. Robust wild plant communities can prevent floods, stabilise soil and provide clean water and air. Coastal salt marshes and mangroves buffer us against storm surges and flooding from the sea. 

Most human communities depend wholly or partly on wild food from the sea and a whopping 3 billion people across the globe rely on wild-caught and farmed seafood as a primary source of protein. In many parts of the world, people obtain wild food, medicines and fuel from natural ecosystems. And, as described earlier, trees and other plants are critical in capturing carbon and storing it in their bodies or in our soils. 

Forest elephants, like other large fruit eaters, play an important role in protecting us from climate change due to their role as 'forest gardeners’. By feeding off smaller shrubs, they ‘thin’ the forest, helping larger slow-growing plant species to survive. These large trees trap and store huge quantities of carbon dioxide from the atmosphere. Forest elephants have been shown to represent a carbon storage service of $43 billion. 

Decimation of plant and animal populations - and loss of species - is greatly compromising these and other benefits that we get from nature. 

15. What are we doing to our wildlife?

Habitat destruction, climate change, overconsumption and pollution, are having a huge impact on the animals, plants and other species that we share our planet with. In fact, the Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES) warned that the current biodiversity crisis is on a par with the threat to humanity posed by climate change.

According to Sir Robert Watson, Chair of the IPBES: “The health of ecosystems on which we and all other species depend is deteriorating more rapidly than ever. We are eroding the very foundations of our economies, livelihoods, food security, health and quality of life worldwide.” 

In 2019, the IPBES Global Assessment used the information the IUCN had gathered on the proportions of known species found to be at risk, along with information on the number of species on Earth, to estimate that a staggering one million animal and plant species are now threatened with extinction due to human action, many within the next few decades. 

16. Are we really entering the Sixth Mass Extinction?

It’s not just how many species we are losing; it’s how fast we are losing them.

Globally, species are going extinct at rates 100-1,000 times faster than the ‘background rates’ typical of Earth’s past. The 400 vertebrate species that went extinct in the last century should have taken about 800 to 10,000 years to disappear naturally. Amphibians are now disappearing at a rate between 1,000 to 45,000 thousand times faster than natural background rates.

Several studies have suggested that things are so bad that we are now entering the Earth’s Sixth Mass Extinction event. Mass extinctions are defined as times when the Earth loses more than three-quarters of its species in a geologically short interval, as has happened only five times in the past 540 million years. 

In the words of Sir David Attenborough: 

“This isn't just about losing wonders of nature. With the loss of even the smallest organisms, we destabilise and ultimately risk collapsing the world's ecosystems - the networks that support the whole of life on Earth.”

17. Can we plant trees to solve the carbon problem?

Trees are an important part of the carbon cycle because they draw down carbon dioxide during photosynthesis, which naturally leads to the suggestion that by planting trees we can remove excess CO2 from the atmosphere. The IPCC in its 2018 report said that an extra billion hectares of forest would be needed to keep temperatures within the “safe” level of 1.5 C. Many tree-planting initiatives have sprung up in recent years, such as the Trillion Trees project. However, planting trees is not a simple solution to our problem.

Trees are complex because they only draw down carbon for part of their life-cycle, when they are growing fast and photosynthesising. At other times they actually return greenhouse gases to the air - for example during the night when there is no photosynthesis (plants breathe out CO2 just like animals do), or after they die if they are decomposed by methane-producing organisms, or if they burn in a fire. The total removal of carbon thus depends on what happens to the tree: to allow a net removal of carbon, the remains of the tree must be somehow prevented from rotting or burning.

It also needs to be kept in mind that planting and nurturing trees is a resource-intensive exercise that itself produces carbon, and consumes water which is an increasingly precious resource. Most important of all is land - we would need to plant out an area the size of Africa to account for just five years of emissions at our current rate of production. Sadly, we cannot plant our way out of the climate crisis.

See Planting trees for a more detailed discussion of the issues

18. So what needs to happen now?

To address the climate and ecological crisis we urgently need to see huge political shifts away from our fossil fuel-based economy. We need fundamental systems change in every industry and in every area of society that is fossil-fuel dependent. We need to also address the emissions that come from changes in land use, reverse deforestation and transform agricultural practices so that we can feed the world without it costing the Earth. It is essential that we take the ecological crisis seriously too, by protecting vulnerable ecosystems and encouraging increases in biodiversity across all parts of the globe. 

All of this would take unprecedented transformation of global economies, the likes of which we have never seen, and that go way beyond the "optimistic policies" laid out by governments so far. 

It will be hard, but it is possible. But it has to come from governmental and collective action; we cannot do this alone.

The banner image represents Global Bio Stripes: https://findingnature.org.uk/ - Data: LPI 2022. Living Planet Index https://stats.livingplanetindex.org/