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The latest United Nations climate report says that humans are unequivocally responsible for warming the atmosphere, land and oceans. The Sixth Assessment Report on the science of climate change by the UN’s Intergovernmental Panel on Climate Change, or IPCC, lays out some very sobering numbers. Global surface temperature has increased faster since 1970 than in any other 50-year period over at least the last 2000 years, but the report says there is still time to act.

The Allegheny Front’s Kara Holsopple spoke with Astrid Caldas, Ph.D., senior climate scientist with the Union of Concerned Scientists about the takeaways of the report. 

LISTEN to the conversation

Kara Holsopple: The report says we have raised the temperature by about 1 degree Celsius since the mid 19th Century, but we can still limit global temperature rise to 1.5 degrees Celsius, which is the goal of the Paris Climate Agreement. What will that take, and how long do we have to do it?

Astrid Caldas: The ideal timing to do that is before mid-century, and the ideal time for most of the actions that are needed is by 2030. To reach that, we are going to need to, of course, increase the use of renewable energy. We’re going to have to decrease and phase out most of the fossil fuel economy, which is gas, coal and oil. 

We’ll need to really change the way we live. But whenever we talk about change, people get worried, right? It’s not a change for the worse. It’s just a change in how we do things. So it’s going to take a big effort, and that effort has to be global, of course.

Holsopple: So about a decade then?

Caldas: You know, we don’t particularly like the idea that you say you have 10 years to do this because there’s no sharp deadline. The earliest we can do it, the better. That’s the main message of the report and the message that climate scientists like to spread.

Holsopple: If we are able to hold global temperature rise to 1.5 degrees Celsius, though,  a lot of damage in terms of climate impacts has been done and will continue, right? We’re not even at 1.5 yet. 

Caldas: No, we’re not. We’re getting there. We are just below 1.1 degrees Celsius currently. And yes, a lot of these impacts from climate change are already baked in, as we call it. Sea level rise has a lot baked in. Extreme heat has already a lot baked in. We have seen increases in the strongest hurricanes in the Atlantic, Category 3, 4 and 5 because of the amount of warming that the oceans are absorbing, and the oceans are getting warmer. That’s an impact that’s going to take a while to reverse. 

It’s not that they cannot be reversed, but it’s unlikely that they can be reversed even if we stop everything right now. What we can do is stop or reduce the rate of increase of these impacts, the the rate of worsening.

Kara Holsopple: This is the first IPCC report to address tipping points. Can you say a little bit about what those would be? 

Caldas: I try to stay away from the language of tipping points, even though this report mentions them, because people get so hung up on the idea of tipping points that they fail to see the possibilities to avoid those tipping points. So it’s like, ‘Oh, we are already there, or we are almost there, so there’s nothing we can do. Let’s focus on something else.’ 

So whenever I get asked about tipping points, I tend to pivot to identifying how much worse impacts are getting year by year, and then work towards reducing those impacts so as to avoid those tipping points that are mentioned in the report. 

But tipping points are basically when you get to a point where it’s irreversible. For instance, corals might disappear completely, depending on the amount of warming that we get and or are going to be reduced greatly. So this would be a tipping point for the corals. 

Deforestation can happen to such a high level, like it’s happening in Brazil. Things can really deteriorate fast. So that’s what they meant by tipping points. But I prefer to stay away from that. 

Holsopple: Is there something in the report that stuck out to you?

Caldas: I think that the most important thing for the conversation and the controversy about climate change, which shouldn’t exist, is that this report mentions how much better the science of attribution has become in the past few years since the last report. 

It used to be that we would say ‘It’s very hard to say that this event was caused by climate change.’ Well, we still don’t say that. But because we have such good models, we can actually say with a certain percentage of certainty how much more likely an event has been made by climate change, and how much more often it could happen.

Holsopple: Like the heat dome over the Pacific Northwest or the flooding in China?

Caldas: Yes, and Hurricane Harvey. Some of these events are becoming much more rapidly assessed, and the science has developed so well that we can really tell a lot more. 

Holsopple: New in this report is more regional information about climate effects and an interactive atlas. How can these tools be used by policymakers?

Caldas: By scaring them? [Laughs] But seriously, it’s really a lot more impactful in the visual, like that interactive tool, as opposed to looking at a graph with all kinds of lines and things. It’s a lot more impactful when you see the colors changing for the increase in temperatures and also when you look at different regions and you see that the impacts are actually distributed around the globe. A lot of people are seeing pretty much the same thing, and a lot of people are seeing a variety of things. 

Another thing that this report mentions is the increase in the probability of compound impacts. It’s not just one thing happening at a time in one place. This thing happens here, another thing happens on top of it that, influencing something else. So there are all these things that are interacting to create worsening situations. 

These regional approaches help us understand how widespread climate change is and how important it is to realize that we are already seeing the impacts of climate change. It’s not something in the distant future.

Holsopple: What is the Union of Concerned Scientists trying to communicate about this report?

Caldas: Not only about this report, but we have for the past few years been very intent on bringing the urgency of the climate crisis to policymakers so that they realize that they have to take action to avoid the worst of climate change. 

This report, on top of various others in the past, just keeps bringing this urgency up and up and up so we can see that the determinations of this report are much more forceful. It’s undeniable. It’s virtually completely certain so the language of this report kind of really tells us that things are getting worse and we need to act. That’s the message that we have been trying to convey for years. 

Holsopple: We talked about policymakers, but how do you hope the general public will receive this information?

Caldas: There are people who are going to freak out. There are people who are going to get more concerned. There are people who are going to jump to action. 

There are people who are just going to not change because they do not accept the science or they fear change. They don’t want to trust the science because they may believe that’s going to change their lifestyle. They may believe that something is going to come up that’s not going to make it so bad. You know, we have relied on technology heavily for our past history. 

People can really request that their policy makers, the elected officials, do something about it. And on the other hand, we should also try to really work on changing our lifestyles while we have the choices to change our lifestyles. That’s a very important point. We can choose to change and not have our lifestyle completely upside down. 

If we let things go into the future, there may come a point where the choices are going to be vastly diminished and we are not going to be able to do everything we wanted to do. We don’t want to look back and say, I should have done something 20 years ago. 

Astrid Caldas, Ph.D. is a senior climate scientist with the Union of Concerned Scientists.