So the climate has always been changing – why make such a fuss about what’s happening now?
It’s all a question of timescale!
The climate of the Earth is (and has always been) naturally fluctuating. Ice ages caused glaciers to cover large areas of the Earth, and many millennia before that temperatures were so warm that there were tropical climates near the North Pole. In the last 800,000 years, climate has cycled between ice ages and periods called interglacials. These cycles seem to last around 100,000 years, and are largely caused by slight changes in the Earth’s orbit.
The problem is, things are happening much quicker now…
The changes we’re seeing in the Earth’s atmosphere are happening much, much faster than the changes that caused the massive climate shifts we’ve seen before. The warming we’re seeing would normally have happened over hundreds of thousands of years. Instead, we’re seeing it over decades. Current warming is more than ten times faster than we would expect to see coming out of an ice age.
So what’s causing this?
The orbital changes over the last few hundred years have been very small, and cannot have caused this warming alone. It is extremely likely (with over 95% certainty) that current warming is due to human activity since the Industrial Revolution.
Evidence that human-produced (anthropogenic) greenhouse gas emissions (GHGs) are the cause is very robust. CO2 levels (amongst other GHGs) have risen by more than 40% in the past 200 years, with much of this stemming from the 1970s. CO2 levels are increasing more than 250 times faster than they did from natural sources after the last ice age.
This rise in CO2 is largely due to the increased burning of fossil fuels, as our society ‘advances’. CO2, amongst other gases such as methane (produced by industrial agriculture amongst other sources), trap heat in our atmosphere. Resultingly, our temperatures are rising – since pre-industrial times, the Earth has warmed by 1°c.
1°c – that’s not very much…
1°c might not sounds like much of a temperature change when you think about the fluctuations that happen daily. However, this warming is already having catastrophic effects on all forms of life. Forest fires are raging, droughts are occurring, extreme floods are destroying people’s homes.
Experts believe we should try and keep warming to below 1.5°c. Previously, they thought it should be 2°c. At 1.5°c, the proportion of the population experiencing water stress could be 50% lower than at 2°c. It’s predicted that corals would have a 90% death rate at 1.5°c, compared to 99% at 2°c. Other risks are highlighted in the figure below.
It doesn’t sound good, and these thresholds for massive devastating impacts keep getting lower, as we get closer and closer to reaching those limits. The climate is warming more quickly than ever before. These are not just natural changes.
- The Royal Society – Climate is always changing. Why is climate change of concern now? – https://royalsociety.org/topics-policy/projects/climate-change-evidence-causes/question-6/
- WWF – 10 myths about climate change – https://www.wwf.org.uk/updates/10-myths-about-climate-change
- Climate Change Committee – A natural climate change – https://www.theccc.org.uk/the-science-of-climate-change/climate-variations-natural-and-human-factors/a-natural-climate-cycle/
- Climate Central – How do we know global warming is not just a natural cycle? – https://www.climatecentral.org/library/faqs/how_do_we_know_it_is_not_a_natural_cycle
- IPCC – Fifth Assessment Report – https://www.ipcc.ch/report/ar5/syr/
- NASA – Climate change: how do we know? – https://climate.nasa.gov/evidence/
- The Guardian – We have 12 years to limit climate change catastrophe, says UN – https://www.theguardian.com/environment/2018/oct/08/global-warming-must-not-exceed-15c-warns-landmark-un-report