The A to Z of Climate Change

A. Adaptation 

Adaptation is the adjustment in natural or human systems to the impacts of climate change. Adaptation is used to describe a wide range of activities and can include physical protection such as the restoration of flood plains, as well as behavioural changes like attempting to save water in drier summers. Wildlife can also “adapt” to climate change, as they try to follow their preferred climate or change how they behave. 

B. Biodiversity 

Biodiversity is the variety of living organisms and how they live and work together in a particular ecosystem. Climate change and biodiversity are interconnected.^[1] Climate change can amplify existing threats and increase biodiversity loss. Biodiversity, through the ecosystem services it supports, also makes an important contribution to both mitigation and adaptation to climate change. 

C. Climate change 

Climate is the long-term average in weather conditions and global temperature over a region; typically measured over a 30-year period. The Earth’s climate has constantly changed throughout history. But since the industrial revolution, higher concentration of carbon dioxide caused by humans, has unequivocally led to global warming and related climate change impacts. Whilst climate change is a long-term effect, it alters short-term weather conditions across the world.

D. Deforestation 

Deforestation is the removal of trees from an area. A staggering 10 million hectares are deforested each year (nearly five times the size of Wales)^[2]. Deforestation and forest degradation leads to the release of carbon stored in trees, making it a big source of man-made greenhouse gas emissions and a driver of climate change. 

E. Extreme weather events

Extreme weather events, such as storms, droughts, and heatwaves, have typically been rare throughout history. However, climate change has increased both the likelihood and severity of many of these events, causing devastating impacts to both people and nature. Recent scientific advances, mean we can now “attribute” how much more likely or severe an extreme weather event has been due to climate change.

F. Food  

Why is food spoken about so much when it comes to climate change? Food and the agriculture system are important drivers of biodiversity loss and climate change. With some estimating a quarter to a third of greenhouse gas emissions come from food systems. Changing patterns of consumption to eat less meat, and reducing food waste, are important ways of cutting emissions from our food system

G. The greenhouse effect  

Sunlight passes through the atmosphere, warming the Earth’s surface. Some of this warmth, or energy, is then re-emitted as infrared radiation. This is where the greenhouse effect comes in. Greenhouse gases in the lower atmosphere prevent this radiated heat from escaping. Essentially trapping heat at the Earth’s surface. Without the natural greenhouse effect, the Earth would be very cold (and not even habitable). But the ongoing emission of man-made greenhouse gases into the atmosphere, is leading to global warming and its adverse impacts.

H. Heat pumps and other climate solutions

Heat pumps transfers heat from the outside air or ground into a building. This process not only uses electricity, which can be sourced from renewable clean energy supplies, but is also highly efficient compared to gas heating. Many climate solutions, like heat pumps, are becoming better and cheaper than ever before. These solutions mean that tackling climate change also means improving our quality of life.

I. Impacts  

Impacts of climate change are becoming more common and closer to home than ever. The worst impacts often felt by countries which have contributed the least greenhouse gas emissions. Climate impacts can be gradual over a long period of time, such as, sea-level rises putting pressure on our houses and businesses around our coastline. They can also be very abrupt and rapid (see Extreme weather events). Climate impacts overseas are also having damaging effects on the UK, raising food prices and threatening our food security.

J. Just transition  

A just transition to a low-carbon and climate-resilient economy is one which is fair, inclusive and not worsening existing inequality. As we switch from high-carbon industries to those which are greener, workers and households need to be provided with the support they need to benefit from this transition. While protecting the environment and creating sustainable economic opportunities. 

K. Keeling Curve  

Named after scientist Charles Keeling, the Keeling Curve was one of the first graphs to demonstrate increased carbon dioxide levels in our atmosphere. Measured at Hawaii’s Mauna Loa Observatory, human activities such as burning fossil fuels, has led to approximately a 30% increase in carbon dioxide from 1958 (when records began) to 2024. The science is clear: there is no doubt that this has caused our planet to warm.

L. Loss and damage  

Climate impacts which go beyond adaption efforts are known as Loss and Damage. One example is a particularly large storm which breaks through existing defences, damaging properties and the environment. Developing countries are particularly vulnerable. To minimise loss and damage, we need to reduce greenhouse gas emissions and ensure we have the appropriate resources and efforts to adapt to climate impacts.  

M. Mitigation  

Mitigation refers to efforts we make to cut the rate of man-made emissions of greenhouse gas into the atmosphere. Climate change mitigation includes actions such as switching from polluting fossil fuels to clean renewable energy sources, improving energy efficiency, lowering consumption, and stopping deforestation.

N. Nature-based Solutions 

Nature-based Solutions are actions to protect, sustainably manage, and restore natural and modified ecosystems, benefiting people and nature at the same time.^[3] Strong and healthy natural ecosystems can absorb greenhouse gases from our atmosphere, build resilience to climate impacts and provide numerous benefits for people and wildlife. Nature based solutions include the protection of salt marshes, the restoration of forest habitats and the adoption of sustainable agricultural management systems. Find out more about WWF's Nature-Based Solutions Accelerator. 

O. Oceans  

The world’s oceans have been a silent guardian of our climate. They have taken up more than 90% of the excess heat in the climate system and absorbed up to 30% of the carbon dioxide we pump into the atmosphere, slowing the impacts of climate change so far.^[4]. However, this has not come without cost. The excess heat is causing marine heatwaves which harm ecosystems and economies.^[5] The absorbed carbon dioxide is causing ocean acidification, which can dissolve shells and impact functioning of marine species, damaging the food chain.  

P. Paris Agreement  

In 2015, the world saw a historic deal come together between 195 countries to address climate change. The most well-known part of the Paris Agreement aims to limit global warming to well below 2°C above pre-industrial levels and to pursue efforts to limit warming to 1.5°C. However, the agreement also highlights several other topics, including the importance of adaptation and international finance. 

The Paris Agreement has widely been considered a success. A primary component of the Paris Agreement is for each country to periodically submit their plans and ambitions to reduce emissions, in documents known as Nationally Determined Contributions or NDCs. Taken these together at the end of 2025, if countries stick to their commitments, are projected to lead to global warming of around 2.3–2.5°C by the end of the century, a considerable improvement from the roughly 4°C trajectory before the Paris Agreement was in place.^[6]

Q. Quantified goal in climate finance 

Climate finance is vital to ensuring that each country can mitigate and adapt to climate change. At the UNFCCC 29^th Conference of the Parties (COP29), the New Collective Quantified Goal (NCQG) was agreed to channel financial support to developing countries for climate action. This set a new target for developed nations to mobilise at least $300 billion of finance annually by 2035, alongside a broader aim to mobilise $1.3 trillion of both public and private finance. Climate finance has historically been one of the trickiest subjects to negotiate on in international negotiations. 

R. Renewable energy  

Renewable, clean, and affordable energy is central to a better future. We need to transform the global energy-system  from one reliant on burning fossil fuels, such as coal, oil and gas, to renewable energy sources, such as wind and solar.^[7] This is not only essential for reducing emissions to tackle climate change, but due to technological advances- renewable energy sources are commonly cheaper than fossil fuel alternative.^[8] While challenges remain, the future trajectory is bright, and innovation means that every day brings a newer, better version of renewable energy systems. 

S. Sea-level rise 

Sea-level rise occurs because warmer temperatures cause ocean water to expand, land-based ice sheets, and glaciers melt. Due to rising temperatures, the global mean sea level increased 20cm between 1902 and 2018 and the sea level rise is getting faster as time goes on. Sea level rise is felt differently across the world, but as an island nation, sea level rise in the UK can significantly increases the area at risk of flooding, the rate at which cliffs are eroding, and how saltwater intrudes into freshwater habitats. Sea-level rise is a very slow process. This means that sea-level rise will continue even if global warming stopped tomorrow, meaning we need to adapt. On a more positive note, our actions on reducing warming now can reduce sea-level rise impacts for centuries to come.^[9]   

T. Tipping points

In certain systems, a relatively small given action may lead to a very large and potentially even irreversible response. The threshold at which that response occurs is known as a “tipping point”.^[10] On Earth, it is thought some large and vital environmental systems - for example, the Amazon Rainforest or ocean circulation in the Atlantic -may fundamentally change if a tipping point in global temperature is exceeded. This would lead to devastating impacts across the world and is perhaps the scariest unknown in climate change.

However, if we take this same concept and apply it broadly to social and economic systems, we can embrace and create powerful solutions. The rise in renewable energy and electric vehicles across the world showcase how, what can seem like a slow process to begin with, can rapidly snowball into something capable of transforming our society. 

U. UNFCCC 

The 1994 United Nations Framework Convention on Climate Change has the ultimate objective to prevent “dangerous” human interference with the climate system. The UNFCCC spawned two further treaties to pursue this objective – the Kyoto Protocol, which entered into force in 2005, and the Paris Agreement negotiated in 2015. 

V. Vulnerability 

The vulnerability of a species or system is a measure of how badly it will be affected by climate change impacts. Vulnerability makes up one of the three pillars of risk, the others being the hazard (what the impact is and how severe it is) and the exposure (how much of the species population or system is affected by the hazard). Species which are more vulnerable are less able to survive under climate change - this maybe because they are more dependent on the climate or that they are less able to escape the changing conditions. 

W. Warming

Human activities have caused ~1.2°C of global warming above pre-industrial levels,^[11] with the  past ten years on record being the warmest on record.^[12] Even though global warming exceeded 1.5°C for the first time in 2024, this does not mean that we have breached the long-term temperature goal set out in the Paris Agreement nor does it change the urgency of limiting warming to 1.5°C to avoid the worst impacts of climate change. Temperature rise varies in different regions of the globe, with warming in the Arctic more than double the global average.^[13] 

X. X 

A rather liberal interpretation of the “X” as stop. According to the IPCC, to limit global warming to 1.5°C, there can be no new fossil fuel projects. We need to stop our dependence on fossil fuels and the subsidies being provided to fossil fuel industries. 

Y. Yearly greenhouse gas emissions 

Global greenhouse gas emissions were estimated to be over 50 billion tonnes in 2024.^[14] In comparison, UK greenhouse gas emissions in 2024 were 414 million tonnes, half of 1990 levels.^[15] However many of the products we use or consume are produced elsewhere in the world. When we consider these emissions our national carbon footprint is significantly higher.   

Z. Zooxanthellae  

Zooxanthellae are algae living in the tissue of healthy coral.  When water is too warm, corals expel the zooxanthellae and turn white in a process called coral bleaching.^[16] Marine heatwaves have resulted in large-scale coral bleaching events at increasing frequency ^[13] with 2014-17 witnessing the most severe, widespread, and longest-lasting global-scale coral bleaching event ever recorded.^[17] 

This A-Z glossary has tried to cover some of the reasons we need to act on climate change now and some issues that climate change encompasses.

Climate change is a global problem, and it is vital we ensure that politicians and business leaders in the UK and around the world continue to see dealing with climate change a priority.