Christmas is a time for getting the whole family together, cracking open the sherry before noon, and having endless debates at the dinner table. But this year, rather than arguing the merits of whether or not Christmas pudding should be served with brandy butter or custard, why not talk about something that’ll have a bit more impact?

The thing about climate change is that it’s not a matter of an opinion. It’s a fact, the climate is changing. By arming yourself with all the facts you can better inform others of the necessity of taking action. So, here’s our handy guide to talking climate change over the dinner table. Hopefully, it’ll answer your questions, and help you better answer those of your family:

Brrrrrrrr it sure is cold out.  Are we sure the climate is changing?  

Now that’s an easy one! We know the climate is changing because global temperatures have increased rapidly, especially since 1980. We’ve got great historical data that clearly shows this. In fact, 14 of the hottest 15 years on record have occurred in the last 20 years. 

How do we know human activity is causing the climate to warm?

As you can see from the graph below, levels of CO2 are now at record levels. This is because of humans burning fossil fuels, which add several billion tonnes of CO2 to the atmosphere every year.

The graph above shows that global temperatures and the levels of CO2 in the atmosphere are pretty closely correlated. But as we know – correlation does not equal causation.

So how can we be sure it’s the CO2 causing this?

First of all, we know it’s not the sun or volcanic activity doing it, which is what some climate change deniers might try and tell you.

We know it’s CO2 causing global warming because we know it reflects heat. We’ve known this for a long time. Since the 1880s in fact. 

You can fill a jar with CO2, put a heat source at one end and a device for measuring heat (thermopile) at the other, and see what happens. When you do, you’ll find CO2 blocks a lot of it from reaching the thermopile ­– that’s because it reflects the heat. That’s the exact reason CO2 warms the earth, because it reflects heat back rather than letting it escape to space, acting like a blanket that warms the earth. 

How do we know exactly how much warming CO2 will cause? 

So, we know for sure that CO2 is causing the earth to warm. But how do we know exactly how much warming it will cause? Scientists haven’t got a test earth to run experiments on, so how can we be sure they are right when they say that we need to get to get net emissions down to zero by 2050 to be in with a chance of keeping global temperature changes within 1.5 degrees C?

We know because of climate models. Scientists build super-accurate models of the earth’s climate by taking real data and simulating the climate with a giant supercomputer. Using computers capable of undertaking over one thousand trillion (a quadrillion) calculations per second, climate scientists can run simulations of the climate in thousands of 100 cubic km cubes mapped across the surface of the earth. 

They factor in a huge range of factors like dust in the atmosphere, the reflectivity of ice, vegetation and more, to build an extremely accurate picture of how the planet will warm in a variety of different scenarios.

But how do we know the climate models are accurate?

You might think it’s impossible to really test climate models, because there is only one earth, so you can’t run an experiment. 

But the great thing about computers is you can give them historic data sets, and let them predict today’s temperature, and see how close they get.

These are called ‘hindcasts’, and they allow scientists to compare model predictions of the past climate to recorded observations of what really happened.

What you see here on the graph above in pink and blue are hindcasts where the model has predicted the climate using historic data based on 2 scenarios, one where human activity causes increased
CO2 emissions, and one that models what the climate would be like without CO2 emissions from humans.

As you can see, the model basically got it exactly right with its predictions for today’s temperature, using only historic data. The black line shows what actually happened to the climate, and it’s bang in the middle of the model’s predictions.

The result is clear – the models are accurate. So, what are they telling us? 

Under a scenario where carbon emissions are somewhat contained, but not brought down to zero (known as RCP 6.0) the models predict that global temperatures will rise by 3 to 4°C. This will have a devastating impact on the environment and biodiversity, as well as causing sea level rise and devastating natural disasters like hurricanes and wildfires. 

Sadly, that’s not even the worst of it. If emissions of CO2 keep increasing, as they have been over the past decades, then the outcome will be even worse. In that scenario, temperatures will increase by 4°C or more and could trigger a climate catastrophe where so much permafrost melts that the methane released will cause a vicious cycle of exponential warming.

What do we need to do to avoid this?

Scientists recommend keeping global temperature rises below 1.5°C to avoid dangerous outcomes. The truth is there’s no entirely ‘safe’ level, climate change is already causing increased wildfires, heatwaves, droughts, floods and more powerful hurricanes. But above 1.5°C or warming these start to get a whole lot worse. 

How can we keep temperatures rises below 1.5°C? 

Greenhouse gas emissions will need to peak before 2030 and then begin a rapid decline, so that the world becomes net zero carbon by 2050.

If we need to be zero carbon by 2050, then it’d be silly building new houses with gas boilers that are locked into using gas heating systems. You’d just have to retrofit them soon after you’d built them. That’s why we built homes so efficient they can be powered by electric heating systems that are powered by energy from 100% renewable sources.

To paraphrase Oscar Goldman in six million dollar man ­– ‘we can do this. We have the technology’. A zero-carbon world is possible. Climate change is caused by humans, so humans have the power to change it. We’ve faced big challenges before, and always over-come then. 

Climate change is scary, but that doesn’t mean we should despair. The sooner we act, the better chance we’ve got. So let people know that the best time to start reducing their carbon footprint is now.

Hopefully, you now know a little more about climate change, but if you’re faced with some common climate myths over Christmas, we’ve got the answers lined up for you:

Myth busting crib sheet

Myth: The climate has changed before naturally, this is probably no different.

Reality: Humans have caused CO2 levels to spike in just a few decades to the highest level in 800,000 years, and it’s causing rapid temperature change. Natural changes in the climate tend to be gradual, taking place over hundreds of thousands of years. We’re changing the climate extremely fast, which means ecosystems can’t keep up with the pace of change.

Myth: It’s the sun, not CO2 that’s changing the climate.

Reality: Solar irradiance has declined slightly since the 1960s. If it was the sun affecting the climate, we’d see temperatures falling, not rising. 

Myth: The models just aren’t reliable. 

Reality: Climate models can consistently predict the temperature correctly using historic data sets.

Myth: Animals and plants will be able to adapt.

Reality: Evolution takes place over thousands of years. Climate change will be causing dramatic changes in decades. Ecosystems won’t be able to adapt, causing mass extinctions. 

Myth: It’s actually cosmic rays.

Reality: There’s been no significant change in levels of cosmic rays over the past 30 years, nor do they significantly contribute to global temperatures.

Myth: It’s the urban heat island effect.

Reality: Urban and rural areas show the same levels of warming.

Myth: It was warmer in medieval times. 

Reality: It is now warmer than it was during the medieval warm period, and temperatures are set to increase far more if we don’t drastically reduce CO2 emissions.

Myth: It’s waste heat from cars, homes and industry, not CO2 that is causing warming. 

Reality: The greenhouse effect adds over 100 times more heat to the climate than waste heat.

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