A climate scientist’s top 5 takeaways from the latest IPCC climate report

Ilissa Ocko

A new climate report is out and it is the most dire yet.

The report is the first installment of the latest climate change assessment by the United Nation’s Intergovernmental Panel on Climate Change. It focuses on the physical science of climate change, and reports on the current state of the climate, possible climate futures, risk assessment and limiting future climate change. Two other reports due out next year will assess impacts to society and ecosystems and strategies to adapt to and mitigate further changes.

Written by more than 200 of the world’s leading climate scientists, the report synthesizes the best available climate science information from more than 14,000 studies.

Below are my top five takeaways from this latest report.

1. Many changes to our planet are accelerating, unprecedented and irreversible

Climate change is affecting every inhabited region across the globe, and some of the impacts are accelerating.

For example, the rate of sea level rise was twice as fast between 2006 and 2018 than it was between 1971 to 2006, and three times as fast as between 1901 and 1971. We are also seeing a faster increase in the amount of rain falling over land areas in recent decades compared to earlier.

The scale of several changes are also unprecedented over centuries and even millenia. Current levels of carbon dioxide in the atmosphere are the highest in at least 2 million years and the last time the ocean warmed this quickly was when the last Ice Age ended.

And many of these changes across the climate system are irreversible over human timescales, such as changes to our oceans, ice sheets and sea level.

2. Human influence on the climate system are the main driver of changes

There is strong confidence that human influence on the climate system is the main driver of retreating glaciers worldwide, the shrinking extent of Arctic sea ice, the declining springtime snow cover in the Northern Hemisphere and a rising sea level.

Further, human-caused climate change has been linked to occurrences of extreme heat, heavy downpours (including hurricanes) and drought conditions. And compound extreme events, such as concurrent heatwaves and droughts, are also found to have been made more likely due to human influence.

3. We may cross the 1.5C threshold earlier than expected

It is likely that we will pass the average 1.5C temperature rise level by 2040, which is about a decade earlier than predicted in the 2018 IPCC report. The difference is in part because we have better estimates of global temperature between 1850 and 1900 (the baseline period for temperature increase), which resulted in scientists determining that the planet has warmed more since this time period than previously thought.

Compared to today, a warming of 1.5C will likely result in intensifying and more frequent heat waves, heavier rainfall and flooding, more severe droughts and more powerful storms.

4. Every increment of warming matters and we can’t rule out potentially catastrophic events

It is possible that we will only be at the 1.5C temperature level temporarily if we take immediate and drastic action to cut climate pollutants. But even with strong action, global temperature will continue to increase until at least midcentury, the glaciers will continue to melt and the sea level will continue to rise throughout this century in response.

In the absence of further climate action, we could exceed 2C of warming around midcentury, with more than 5C by end of century. The last time the planet sustained 2.5C level higher than 1850-1900 levels was 3 million years ago.

Every additional 0.5°C of global warming clearly worsens extreme events, and all regions are vulnerable, and elements of society and ecosystems worldwide will be impacted.

We also cannot rule out low-likelihood but catastrophic events such as ice sheet collapse and abrupt ocean circulation changes, which increase in risk the more the planet warms.

5. We know what we need to do and the earlier we act the better

Given that every increment of warming matters, it is never too late to act. However, the earlier we act, the better off we will be, and the more devastating consequences we will avoid. And we know exactly what needs to be done.

We need to stabilize our climate in the long run, which will require net-zero carbon dioxide emissions at a minimum. Scientists continue to improve estimates of how much carbon dioxide we can emit to limit warming to desired temperature levels, which can guide policies.

Methods to remove carbon dioxide from the atmosphere are promising for balancing out any residual CO2 emissions, but side effects must be considered, such as impacts to water and food security.

We also need strong reductions in non-CO2 greenhouse gases, most prominently methane. This would have the benefit of slowing down the rate of warming, improving air quality and counteracting increased warming from air quality measures that reduce cooling pollutants.

The bottom line is that even though this report is full of doom and gloom, it is not too late to act. In a year defined by searing heatwaves, torrential floods and raging fires it is encouraging that this same report offers the seeds for a strategy to alleviate some of its most devastating projections.