Key Takeaways:
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Greenhouse gases trap heat in the atmosphere (The Greenhouse Effect). More greenhouse gases = more heat.
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Net Zero is where the amount of greenhouse gases released into the atmosphere (emissions) is balanced with the amount being removed (drawdowns). For several thousand years before the Industrial Revolution the planet was in this state of relative balance and we must return to it to stop further warming.
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Human activity, mostly through burning fossil fuels, has disrupted this balance meaning there are increased quantities of greenhouse gases in the atmosphere.
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These additional gases are causing the planet to warm which is changing the climate.
Additional Greenhouse Gases
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Global Warming
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Climate Change
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The more warming, the more inhospitable many parts of the Earth will become. The quicker the warming, the more difficult it will be for life on earth to adapt (including us).
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What's the goal? Stabilising global temperatures at 1.5°C above pre-industrial levels is the target to avoid many of the worst impacts of climate change, including negative impacts on the economy, and giving us the best chance of avoiding “uncontrolled climate change” (the point of no return which must be avoided).
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What are the likely consequences of climate change? Food scarcity, drought, biodiversity loss, extreme weather, sea level rise, health impacts and war/ conflict (related to migration/resource shortages) are the main concerns. The same thing holds true for all of them… the larger the gap between emissions and drawdowns, the more the warming, the more likely they are to occur and the worse they are likely to be.
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Carbon Budgets: how long have we got? The IPCC estimates that if we continue emitting at the current rate, we will exceed 1.5°C of warming in around 10 years (from 2020). Again, the larger the gap between emissions and drawdowns, the quicker we eat up our carbon budget for any warming threshold. If we reduce emissions quickly now, we buy more time.
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The Detail
What are greenhouse gases?
Greenhouse gases have a warming effect on our planet as they trap heat within the earth's atmosphere, in a similar way to glass in a greenhouse (The Greenhouse Effect). They allow solar radiation from the sun to warm the surface of the Earth, while preventing the infrared radiation (heat) from escaping. The Greenhouse Effect has been necessary for bearable living conditions on Earth (as otherwise the planet would be too cold) but changing concentrations of greenhouse gases in the atmosphere are causing the planet to warm quickly.
The effect of each gas on climate change depends on three main factors*:
What are greenhouse gases?
Greenhouse gases have a warming effect on our planet as they trap heat within the earth's atmosphere, in a similar way to glass in a greenhouse (The Greenhouse Effect). They allow solar radiation from the sun to warm the surface of the Earth, while preventing the infrared radiation (heat) from escaping. The Greenhouse Effect has been necessary for bearable living conditions on Earth (as otherwise the planet would be too cold) but changing concentrations of greenhouse gases in the atmosphere are causing the planet to warm quickly.
The effect of each gas on climate change depends on three main factors*:
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Concentration - how much is in the atmosphere? Generally measured in parts per million (ppm) or parts per billion (ppb).
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Lifetime - how long do they stay in the atmosphere?
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Global Warming Potential (GWP) - how strong is their impact?
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The main greenhouse gases responsible for global warming are*:
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Carbon Dioxide - despite relatively low GWP, CO2 is the most prominent gas due to very high concentrations & long lifetime (potentially hundreds to thousands of years). Carbon Dioxide emissions continue to contribute the most to global warming.
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Methane - is the second most prominent gas due to high GWP (around 28 -36 times more powerful than CO2 over a 100 year period) & high concentrations. However, methane is short lived (around 12 years).
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Nitrous Oxide - is the third most prominent gas due to even higher GWP (265 -298 times more powerful than CO2 over a 100 year period) & lifetime (over 100 years).
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Human created (not naturally occurring) fluorinated gases have a smaller but significant impact.
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For simplicity, greenhouse gases are often expressed as a single measure (“carbon dioxide equivalents”).
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Water vapour is actually the most abundant greenhouse gas, but human activity has a small direct influence. However, warmer temperatures means more water will evaporate and stay in vapour form, which contributes to further warming (an example of a “positive feedback”).
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What’s the issue?
For over 5,000 years our planet was in a state of relative balance. Before the Industrial Revolution, the carbon dioxide emitted through respiration and decaying organic matter (dead plant and animal life) was balanced with the amount of carbon dioxide being absorbed by plants through photosynthesis (The Carbon Cycle). Some organic matter, and therefore carbon, gets locked up in the soil and eventually forms fossil fuels.
For over 5,000 years our planet was in a state of relative balance. Before the Industrial Revolution, the carbon dioxide emitted through respiration and decaying organic matter (dead plant and animal life) was balanced with the amount of carbon dioxide being absorbed by plants through photosynthesis (The Carbon Cycle). Some organic matter, and therefore carbon, gets locked up in the soil and eventually forms fossil fuels.
Carbon emissions were roughly balanced with carbon drawdowns (otherwise known as Net Zero). This resulted in a period of stability that allowed life on earth to flourish. There is little doubt that humans have benefited enormously from this stability (the graph below illustrates how stable temperatures have been for several thousand years before the Industrial Revolution and how rapidly it is warming now). We must return to Net Zero in order to limit further warming.
Figure 2 | Changes in the global average temperature over the past 24,000 years. Osman et al. The shaded area represents a 95% confidence interval.
The problem we face now is that human activity since the start of the Industrial Revolution has significantly disrupted that balance. At any given second there are millions of cars, hundreds of thousands of planes, trains, boats, and factories releasing carbon into the atmosphere. Over decades and centuries, this accumulation has led to significantly higher concentrations of greenhouse gases in the atmosphere.
These additional greenhouse gases are trapping more heat within the Earth’s atmosphere and the warming is causing changes to Earth's systems and climate. It is clear from the science and events already happening that the negatives of warming the planet will far outweigh any positives (i.e. more carbon = more warming = more bad news) and therefore we should do everything we reasonably and realistically can to get to Net Zero as quickly as possible (see What’s the Situation?).
These additional greenhouse gases are trapping more heat within the Earth’s atmosphere and the warming is causing changes to Earth's systems and climate. It is clear from the science and events already happening that the negatives of warming the planet will far outweigh any positives (i.e. more carbon = more warming = more bad news) and therefore we should do everything we reasonably and realistically can to get to Net Zero as quickly as possible (see What’s the Situation?).
Additional Greenhouse Gases
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Global Warming
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Climate Change
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The problems are exacerbated by the current speed of warming. Obviously it would be politically and economically impossible to stop burning fossil fuels overnight and we must find a sustainable balance when determining how fast to transition to Net Zero. The speed of that transition needs to be determined…
In order to act in our best interest and make informed decisions there are a number of questions we should attempt to answer. These are laid out below.
In order to act in our best interest and make informed decisions there are a number of questions we should attempt to answer. These are laid out below.
What’s the goal?
Why this is important: It’s vital that we know what the goal is and where it lies, otherwise it is impossible to formulate a plan to reach that goal and measure progress. We need to have warming and emission/drawdown targets to work towards when considering what we need to do and by when. It is key that the general public know the goal if they are going to hold governments accountable to sticking to it.
After decades of research and given where we are now, scientists are in general agreement that we don’t want to go above 1.5°C of warming (COP26 resulted in increased focus on this target from all countries).
Why?
The impacts of climate change will continue to get worse as the planet warms, but most scientists believe that the worst impacts of climate change can be avoided if we keep global warming below 1.5°C. Even from a pure economic standpoint the benefits of limiting warming to 1.5°C will likely far outweigh the cost of transitioning to Net Zero.
In addition to this, there is a higher risk of “uncontrolled climate change” the more, and quicker, we warm the planet, providing extra incentive to stick to emission targets.
What is “uncontrolled climate change”?
This is the scenario where it becomes unlikely, or impossible, to effectively combat positive feedback loops, meaning global temperatures spiral to a new equilibrium point. If we reach this “point of no return” we could face increasing global temperatures throughout this century and therefore increasingly worsening impacts from climate change (we don’t want to go there).
In reality, it is incredibly complex to estimate exactly where (or if) the “point of no return” exists or what the new equilibrium temperature would be (potentially 4ºC or more). There are thousands of interrelated factors and many tipping points to consider, some of which are poorly understood and many impossible to accurately predict.
Positive feedback loops reinforce an initial change in temperature, some major concerns are:
Why this is important: It’s vital that we know what the goal is and where it lies, otherwise it is impossible to formulate a plan to reach that goal and measure progress. We need to have warming and emission/drawdown targets to work towards when considering what we need to do and by when. It is key that the general public know the goal if they are going to hold governments accountable to sticking to it.
After decades of research and given where we are now, scientists are in general agreement that we don’t want to go above 1.5°C of warming (COP26 resulted in increased focus on this target from all countries).
Why?
The impacts of climate change will continue to get worse as the planet warms, but most scientists believe that the worst impacts of climate change can be avoided if we keep global warming below 1.5°C. Even from a pure economic standpoint the benefits of limiting warming to 1.5°C will likely far outweigh the cost of transitioning to Net Zero.
In addition to this, there is a higher risk of “uncontrolled climate change” the more, and quicker, we warm the planet, providing extra incentive to stick to emission targets.
What is “uncontrolled climate change”?
This is the scenario where it becomes unlikely, or impossible, to effectively combat positive feedback loops, meaning global temperatures spiral to a new equilibrium point. If we reach this “point of no return” we could face increasing global temperatures throughout this century and therefore increasingly worsening impacts from climate change (we don’t want to go there).
In reality, it is incredibly complex to estimate exactly where (or if) the “point of no return” exists or what the new equilibrium temperature would be (potentially 4ºC or more). There are thousands of interrelated factors and many tipping points to consider, some of which are poorly understood and many impossible to accurately predict.
Positive feedback loops reinforce an initial change in temperature, some major concerns are:
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Forest Dieback: climate induced conditions cause large areas of forest to “die”, releasing carbon dioxide and reducing drawdowns. This contributes to more warming, further exacerbating the issue.
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Ice Albedo Effect: warming melts snow & ice meaning less solar radiation is reflected back into space and more heat is absorbed by the earth. This contributes to further ice loss and contributes to more warming.
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Permafrost Melt: warming causes once frozen ground to release methane (a greenhouse gas), contributing to more warming and further permafrost melt.
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Water Vapour Effect: warming creates more water vapour (a greenhouse gas), trapping more heat in the atmosphere. This causes further evaporation, leading to more water vapour contributing to further warming. This is closely related to and partially countered by the Lapse Rate Feedback (which gets quite technical).
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Negative feedbacks lessen an initial change in temperature, the most important feedback is:
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The Planck Response (sometimes referred to as “The Direct Response” or the “Stefan‐Boltzmann’s Law”): the higher the temperature of the earth, the more energy it radiates (which has a cooling effect). This is the same for any object, the hotter it is, the more energy it emits and the quicker it cools if there is no input of energy. This is a significant negative feedback.
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Examples of other "tipping points" include:
- Ocean circulation
- Social/ political tipping points (how humans will react to changing circumstances)
What are the likely consequences of climate change?
Why this is important: We can only begin to assess what changes are reasonable to make if we understand the likely consequences of failing to make enough changes.
Primary (direct) consequences
Why this is important: We can only begin to assess what changes are reasonable to make if we understand the likely consequences of failing to make enough changes.
Primary (direct) consequences
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Extreme Weather- due to more heat energy in the Earth's atmosphere there is already a trend of more frequent and stronger storms, heavier rainfall, longer and more extreme droughts and heatwaves. This trend will continue if we continue to warm the planet.
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Sea Level Rise- warming oceans and ice melt is rising sea levels. This results in coastal flooding, worsening storm surges and some land disappearing altogether.
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Secondary (indirect) consequences
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Food Scarcity- more extreme conditions or different conditions to what livestock and crops are used to is not good for food production. The faster we warm the planet the harder it will be to adapt to changing conditions.
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Water Scarcity- changing rainfall patterns and more extreme droughts/ heatwaves are likely to result in water shortages in parts of the world.
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Biodiversity Loss- changing the conditions in which animal and plant species have evolved to thrive will generally have negative impacts on their chances of survival. It is estimated that the natural world provides trillions of dollars worth of value to human life every year, most of which we take for granted and much of which we’ll start to lose if we continue to warm the planet.
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Coral bleaching- corals get a specific mention as they are particularly sensitive to a warming planet. The IPCC estimates that at 1.5°C of global warming the world will lose “70–90% of reef-building corals compared to today, with 99% of corals being lost under warming of 2°C or more above the pre-industrial period.” Coral reefs provide benefits for around a billion people around the world as well as billions in free services to the tourism and fishing industries. It would be tragic on many levels to lose these marine ecosystems.
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Health- The World Health Organisation (WHO) recognises that climate change is “the biggest health threat facing humanity”. Climate change is already impacting health in many ways, including death and illness from increasingly frequent extreme weather events, the disruption of food systems, increases in food, water & vector-borne diseases, as well as mental health issues.
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War/ Conflict- It is difficult to assess the probability of war/conflict under different warming thresholds but unfortunately it is a real risk that should be considered due to resource scarcity/distribution and mass migration (caused or exacerbated by climate change).
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With all of these impacts the same thing holds true; the larger the gap between emissions and drawdowns, the more warming, the worse the consequences will be from climate change.
How long have we got?
Why this is important: In order to determine when and how quickly we need to make the changes scientists advise, we need to know how long we’ve got until we cross the target threshold.
The key concept to understand here is carbon budgets. I.e. “How much more carbon can we add to the atmosphere before we reach a certain warming limit?”
In their latest report, the IPCC estimated that to have a 50% chance of remaining below 1.5°C of warming, the remaining carbon budget is around 500 GtCO2 (from 1 January 2020)*. Given current annual carbon emissions are around 50 GtCO2 that gives around 10 years at current annual emissions, hence the urgency to act.
In reality, calculating the carbon budget is complex and there is a reasonable level of uncertainty around these figures. Regardless, the larger the gap between emissions and drawdowns, the quicker we eat up our carbon budget for any given threshold.
Graph below: IPCC carbon budgets start in 2018, the part in red shows the budget that was used up in 2018 and 2019. The % next to the “°C” is the probability of staying below that threshold.
Why this is important: In order to determine when and how quickly we need to make the changes scientists advise, we need to know how long we’ve got until we cross the target threshold.
The key concept to understand here is carbon budgets. I.e. “How much more carbon can we add to the atmosphere before we reach a certain warming limit?”
In their latest report, the IPCC estimated that to have a 50% chance of remaining below 1.5°C of warming, the remaining carbon budget is around 500 GtCO2 (from 1 January 2020)*. Given current annual carbon emissions are around 50 GtCO2 that gives around 10 years at current annual emissions, hence the urgency to act.
In reality, calculating the carbon budget is complex and there is a reasonable level of uncertainty around these figures. Regardless, the larger the gap between emissions and drawdowns, the quicker we eat up our carbon budget for any given threshold.
Graph below: IPCC carbon budgets start in 2018, the part in red shows the budget that was used up in 2018 and 2019. The % next to the “°C” is the probability of staying below that threshold.
Source: IPCC
PwC's Net Zero Economy Index illustrates how quickly we need to decarbonise the world economy in order to remain within the 1.5 and 2 degree carbon budgets. A huge ramp up in global efforts is required to keep these goals alive.
PwC's Net Zero Economy Index illustrates how quickly we need to decarbonise the world economy in order to remain within the 1.5 and 2 degree carbon budgets. A huge ramp up in global efforts is required to keep these goals alive.
*From the IPCC Report “Climate Change 2021: The Physical Science Basis”, the Working Group I contribution to the Sixth Assessment Report. Table SPM.2 - Estimates of historical carbon dioxide (CO2) emissions and remaining carbon budgets.