The rate at which the climate is changing is unprecedented in at least two thousand years and possibly much longer. In addition, some aspects of climate change threaten to become irreversible for a period of centuries or even thousands of years, such as rising sea levels. Without drastic measures, the world must prepare for significantly greater weather extremes.
This is evident from the latest report from the IPCC, the United Nations climate panel. A few hundred climate scientists from 66 countries have worked on it for years. It serves as a basis for climate policy by governments worldwide, and comes just ahead of next autumn's global political climate summit in Glasgow.
Since the previous regular IPCC report in 2013, knowledge about the climate has increased considerably. According to climate scientists, it is clear that global warming has already led to major changes: in the atmosphere, on land and in the oceans.
Warming has an effect on weather extremes and, according to the IPCC, the evidence for this is stronger than in the previous report. This includes, for example, heat waves, heavy rainfall, extreme drought and tropical cyclones. The report also states that oceans are warming at an unprecedented rate.
Drastic measures
Over the past two weeks, government delegations from around the world have agreed word for word on a summary of the IPCC report. Scientists always had a right of veto if, in their opinion, the much more extensive underlying report – which consisted of thousands of pages – was being violated. This course of events is always the same. The idea is that countries will embrace the report and use it as a starting point for their climate policy.
If the Earth continues to warm, this will lead to even greater changes in the climate. This mainly means:
- More intense and frequent heat waves
- More heat waves in the oceans
- More and more frequent heavy rain
- More frequent drought
- More severe tropical cyclones
- Less and less ice at the North Pole
- Decrease in permafrost
Source: IPCC
The Earth has warmed by just over one degree since pre-industrial times. In any case, according to the report, warming will continue until the middle of this century, even if we succeed in drastically limiting emissions of CO2 and other greenhouse gases. Only if drastic and large-scale measures are taken quickly, a limitation to 1,5 or two degrees of warming is still possible, the IPCC states.
For the Netherlands, insights into sea level rise are particularly important. It's going faster and faster. Between 1901 and 1971 it was 1,3 millimeters per year, then it became 2006 until 1,9 and then the increase increased to 3,7 mm per year (until 2018).
This means that sea level rise is now most likely faster than at any time in at least the past three thousand years. How much more this will become in the future depends mainly on how quickly it will be possible to reduce emissions. Scenarios show that the average sea level rise at the end of this century varies between a few decimeters to just over a meter (1,01 m).
The UN climate panel IPCC publishes a comprehensive report in three parts every few years, the last time was in 2013. This first part contains the scientific basis for climate change. Parts two and three will be published next year, about the consequences of climate change and about the options for reducing greenhouse gas emissions as quickly as possible.
If everything goes wrong and greenhouse gas emissions remain high, the sea level will continue to rise. In the year 2100 it could be a maximum of two meters, and in 2150 it could be five meters. But, the report states, a much higher sea level rise is also possible “in a scenario with very high greenhouse gas emissions”. This scenario of two meters at the end of this century, five meters in 2150 and fifteen meters in 2300 is not very reliable, but “cannot be excluded due to the high uncertainty in ice sheet processes”.
What is new in this IPCC report is that more attention has been paid to regional differences. The Earth's climate does not change in the same way everywhere. For example, the Mediterranean is mentioned as one of the areas at risk of extremely high temperatures in the future.
Moreover, there is now more clarity about so-called climate sensitivity. That is, the extent to which the climate responds to a certain amount of emissions. The chance that this effect will not be too bad has become considerably smaller.
It is also about possible tipping points in the climate, such as the collapse of one of the large ice caps or abrupt changes in ocean currents. The chance of this happening is considered very small, but it cannot be ruled out either.
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