Climate has always changed. Standing here in the Brecon Beacons is a reminder of that, with valleys like this being gouged out by ice that is no longer here. Each of the last three decades have been the warmest since records began, with temperature records broken in 2014, 2015 and 2016. We have seen a rise in sea levels and in the frequency and intensity of extreme weather events such as floods and droughts. In 2015, 196 countries signed the Paris Climate Change Agreement in order to limit dangerous climate change to well below 2 degrees Celsius.
Two degrees doesn’t sound like a lot, but looking at the Earth’s past we see evidence that such small average temperature changes have led to substantial changes in sea level, and ice and vegetation cover. The last time this valley was covered in ice the temperature was just 4 degrees lower than today. How do we know, then, that the changes we see happening today aren’t just part of the natural process of climatic change on our planet? One way is to look back through the geological past. Hundreds of millions of years ago, what did the planet look like?
The continents were in different positions, the concentration of the carbon dioxide in the atmosphere was much greater and it was a lot warmer, and, for much of the time there was no ice at either of the poles. Greenhouse gases like carbon dioxide insulate the earth by trapping heat. Plants, like these trees here, take up carbon dioxide from the atmosphere as they grow, and release it again as they die and decompose. Over millions of years, instead of decomposing, a lot of plant material became stored as coal and oil.
If we then go back just a million years, the time period over which humans evolved, with the continents in the positions they are now, what was the planet like? To answer that we can to look at more recent records of Earth’s climate preserved in ice. As layers of ice here in Arolla formed tens to hundreds of thousands of years ago they trapped tiny bubbles of air which we can analyse to tell us about past atmosphere and temperature. Temperature and greenhouse gas concentrations were changing but within tight bounds, flip-flopping between glacial and interglacial periods.
These periods are driven by slight wobbles in the orbit of the earth, changing the distribution of sunlight the surface of the planet receives, and leading to feedbacks between greenhouse gas concentrations and climate. Over the last 150 years we have seen greenhouse gas concentrations and global temperatures rise out of these tight bounds to higher levels and at a rate quicker than the Earth has experienced in the last million years. What do you think has caused this? During the industrial revolution, around 1750 to 1840, humans started burning coal and oil on an increasingly large scale, improving quality of life for humankind, but releasing the buried fossil carbon back into the atmosphere at an increasingly rapid rate.
Humans have also converted a third of the planet’s land surface to agriculture, losing carbon stored in forests and soils. Other greenhouse gasses such as methane and nitrous oxide are also produced from agriculture and from industrial activity. So, is it really such a bad thing to feed ourselves, keep ourselves warm, travel to work and visit family and have access to all the exciting, new technology? Is it really our fault that climate is changing, and if it always changed, why should we care now?
According to the overwhelming consensus of scientific experts, the increase of one degree celsius in global average surface temperature that we have already seen has been caused by human activity, and we are already seeing the impacts of this increase. The impacts you will experience depend on where you live. Many of the changes will be catastrophic, but not all. Longer growing seasons, floods, droughts and heat waves, increasing cost of insurance, abandoning your coastal home due to rising sea level. What changes have you already noticed? How much climate changes is in the future is difficult to predict as it depends on the decisions we make now at individual, national and international level.
How do we, as one planet, negotiate a solution that works for all? Climate justice and climate finance are critical issues in these negotiations. Different countries have different historical responsibilities for past and future greenhouse gas emissions, but also experience different levels of change, and have different abilities to adapt to and mitigate the consequences. Imagine you are negotiating for your country, or a country on the other side of the world as these students are doing. What would be your negotiating stance?
To limit warming to two degrees, as countries agreed to in Paris, we will all need to make a massive transformation to low carbon energy. Many countries have already started the transition to low carbon energy and still have high growth in GDP. Land use also has a role to play, not only in reducing deforestation. Intact forests and other land absorb about a third of all anthropogenic carbon dioxide emissions. So preventing deforestation and promoting sustainable afforestation has other co-benefits such as biodiversity and flood control. It takes a lot of land and feed to produce meat, so reducing meat consumption is an individual action we can all take.
Other things we can do to reduce our carbon footprint include insulating our homes, using energy efficiently and walking, biking or taking public transport. These solutions also have co-benefits for air pollution and health, and may save us money. The collective choices we make will control our future climate. What will you choose to do?