Climate change FAQs

Your climate change questions answered. By Anna Mouton.

1.   This winter saw excellent chill accumulation and heavy rainfall in the Western Cape. Why should we worry about global warming?

Weather is more variable than climate. Weather is defined as the state of the atmosphere at a particular time and place. We’ve all experienced how it can change within a few hours or differ between places only a few kilometres apart.

The climate is an area’s long-term — typically spanning decades — average weather. Simple logic tells us that half of all years will be colder or wetter than average.

The problem with climate change is that average temperatures are rising. The average surface temperature for the Western Cape has increased by almost 0.1 °C per decade for the past 100 years. This means that cold winters will become less frequent.

Figure 1 illustrates the effect of warming on winter chill using a hypothetical region where annual positive chill units have decreased from 500 to 450 under climate change. Cold winters in some years don’t mean the climate hasn’t warmed when those cold winters happen less and less frequently.

Figure 1: The reduction in the probability of cold winters under climate change in a hypothetical region.

2.   How can we make long-term climate predictions if we can’t even forecast the rain next winter — or next weekend?

Weather forecasts aim to predict weather conditions for a specific place and time. This is like trying to predict precisely how many minutes and seconds it will take you to drive to work on a particular Wednesday one week from today. We all know that the precise time will vary depending on the day’s conditions.

Climate models investigate questions about long-term trends — more like how long it usually takes you to drive to work. Most people can estimate this fairly accurately because it involves averages.

Scientists build climate models from mathematical equations that describe underlying physical processes. They test the models by inputting climate data from the past and comparing the model’s results to observations from the real world. A model that can extrapolate from the past to the present should be able to extrapolate from the present to the future.

Climate models have also been around long enough that we can see whether past predictions have materialised — they largely have. One example comes from a 2019 study by Zeke Hausfather and colleagues that compared global temperature projections from climate models published in 1970–2007 to recent temperature observations. The authors concluded that 14 of the 17 models generated correct estimates.

Similar accuracy has been shown for other variables, such as sea-surface temperatures and sea-level rise.

3.   The climate varies from year to year and according to cycles such as El Niño. Previous periods were warmer than now — why is the current climate change any different?

Events like El Niño do affect global temperatures but only have short-term effects. El Niño is a localised warming of surface water in parts of the Pacific. Its counterpart — La Niña — is localised cooling of the surface water. These two cycles alternate and may affect weather in other parts of the world, but they don’t produce consistent warming over time.

Current global warming is exactly what the name says: the whole planet is affected. This can only happen if our atmosphere is trapping more solar heat. And rapid warming due to higher levels of atmospheric greenhouse gases has indeed occurred in the past.

One example comparable to current global warming occurred 250 million years ago when atmospheric carbon dioxide levels rose from about 400 ppm to 2 500 ppm, and global temperatures increased by about 8 °C. The carbon dioxide releases were spread over tens of thousands of years, but the amounts per century were similar to today’s carbon dioxide emissions.

This global warming event coincided with the onset of the late-Permian extinction — the most severe extinction in the history of life on Earth. Scientists estimate that 81% of marine species and 70% of land vertebrates died out and that it took 30 million years for the numbers and diversity of land vertebrates to recover.

4.   Living organisms are good at adapting and have adapted to past climate change. Why won’t they just adapt to the current climate change?

Short-term adaptation to climate change usually means migration. This is already happening with many species that can migrate, moving about six kilometres poleward per decade. Not all species are mobile, migration only works if you can find food and space at your new location, and migration isn’t a long-term solution because, eventually, you run out of road.

In the past, living organisms adapted to natural climate change by evolving into new species. But evolution is a slow process, so rapid climate change leads to mass extinctions such as the late-Permian extinction described above.

Humans will face the same challenges as other living organisms. Current atmospheric carbon dioxide levels last occurred about 4.1–4.5 million years ago when the earliest humans had not evolved.

Modern human populations are concentrated in areas with mean annual temperatures of 11–15 °C. Archaeological evidence shows this has been true for at least 6 000 years. Our domesticated plants and animals are adapted to the same narrow temperature range that we are.

Different studies have reported that higher temperatures are detrimental to human ability for physical and mental work, and economic productivity is highest in populations living in a mean annual temperature range of 11–15 °C.

A 2020 study by Chi Xu and colleagues demonstrated that unmitigated climate change will expose about a third of the world population to mean annual temperatures above 29 °C — conditions currently mostly found in the Sahara — within the next 50 years. Humans will likely adapt by migrating, which will create a different set of challenges.

5.   Global warming will lead to longer growing seasons, and higher atmospheric carbon dioxide levels are good for plants. Surely this is good for agriculture?

Global warming will improve growing conditions for certain crops in certain places, but it will not improve conditions for pome- and stone-fruit production in most areas where South Africans currently grow them.

Plants do not live by carbon dioxide alone. Water is one of their other needs. And they suffer when exposed to excessive heat.

A recent study showed that climate change already leads to record temperature highs in all deciduous-fruit production areas. This creates problems ranging from insufficient winter chill and poor fruit set to increased sunburn and lack of red colour development.

Although rainfall may not decrease, higher temperatures drive greater water demand through increasing evapotranspiration. Meanwhile, growers will face more competition from other users for available water resources.

6.   How do we know that human activities cause climate change? Are we sure it isn’t caused by solar activity?

Satellite-mounted instruments have measured the sun’s energy output for around 40 years. It varies by about 0.15% during each 11-year sunspot cycle and has decreased slightly from the early 1970s until today.

So no, the sun isn’t causing global warming by producing more heat. Climate change is also not caused by aerosols, soot, ozone, cosmic rays, nuclear testing, satellite radio transmissions, or breathing.

A scientist first speculated about the greenhouse effect — even though it wasn’t called that — nearly 200 years ago. It was experimentally confirmed in 1859 by researchers interested in understanding past ice ages. The risk of global warming due to fossil-fuel emissions was already recognised before 1900.

Nearly a century of data confirms that the planet is warming, and atmospheric carbon dioxide levels are rising. Analysis of atmospheric carbon dioxide clearly shows that most of it comes from burning fossil fuels.

Human activities emitted around 44 000 million tonnes of carbon dioxide from fossil-fuel use in 2019 alone. Compare this to the 180–440 million tonnes released by all the world’s volcanoes in a year — at most 1% of fossil-fuel emissions — and you begin to appreciate the unprecedented scale of human impacts.

More resources

Climate Action Tracker

Our World in Data

Skeptical Science

World Weather Attribution