Hasn’t climate change always happened?

This was one of the most common questions we received.

“Yes, climate has always changed through things like solar cycles, orbit of the earth and natural variability,” Dr Grose said.

“It’s not a matter of one or the other, it’s a matter of both.

“The rate of change due to humans is more rapid than any previous examples from things like ice age cycles.”

Dr Corney pointed out that current CO2 levels were 414 parts per million.

“We have seen that in the geological record, but not for millions and millions of years,” he said.

“To change from say 300 parts per million to 400 parts per million would take tens of thousands of years.

“We’ve now seen that change in a little over 100 years.”

Dr Melbourne-Thomas said damage to coral was one of the best examples of how rapid the effects of climate change were.

She said it was not possible for corals to move further south to survive.

“Corals can’t move, they are stationary,” she said.

“They can disperse by ocean currents, but whether or not they’ll be able to do that is an open question.”

Dr Melbourne-Thomas said coral was affected by more than just ocean temperature.

“They are being hammered by many angles as a result of climate change.”

Dr Lenton said he accepted that corals were adaptable.

“But one of the challenges here is we don’t know what the adaptive capacity is,” he said.

“The rates that they’ll need to adapt exceeds what we’ve been able to calculate previously.

“Are we going to wipe out corals? No. But the Great Barrier Reef as we know it today will be a completely different place.”

The scientists said the human body — in which a 2 degree Celsius increase meant a person would be very unwell — provided a useful analogy to understand the impact of temperature change in the environment.

Dr Corney said people often commented that a slight change in temperature wasn’t a bad thing, especially for those living in southern Australia.

But he said such a change would result in more heat waves and bushfires like Tasmania experienced last summer.

“There’s a much greater increase in extreme events,” he said.

“Just a couple of degrees warmer and the chances of really long heatwaves increase dramatically.

“We’ll see bushfires like that occur more in the future.”

Dr Melbourne-Thomas said while society may not be “doomed” the world does need to act quickly to address climate change.

“More and more of the evidence is suggesting if we don’t act now we face some pretty serious consequences in the near future,” she said.

Dr Corney said the longer the planet waited to make changes, the worse the consequences would be.

“We’re most definitely not doomed — climate change is not going to end life on earth or civilisation for humans,” he said.

“But it is likely to have some pretty big consequences for wild ecosystems and for civilisations.”

Dr Grose said humans were tenacious and would find ways to adapt.

“We’ve rebuilt after world wars, people do a lot of good work to overcome problems,” he said.

“We need the best minds and organisations working together, but I’m optimistic.”

Dr Corney said he enjoyed engaging in discussions about whether climate change was a real thing.

“I’ve been to plenty of family functions where people want to know if climate change is real,” he said.

“I enjoy that aspect of being able to explain how we have pretty strong evidence that climate change is happening.

“Most people when they sit down and engage in that conversation react well.”

He said some people were reluctant to accept bad news.

“People are scared of change especially when that change is negative,” he said.

Dr Lenton said it he found it challenging working in the climate change space, and was concerned for the future of his children.

“We’d love nothing more than a breakthrough that said the climate wasn’t warming,” he said.

“We’re really hoping we haven’t got it right, but the weight of evidence says we are on the side of the truth here.”

Dr Grose said most people communicated on the issue in good faith, but the spread of false information was of concern.

“It’s a very threatening situation,” he said.

He said because the issue threatened industry and innovation and the way decisions were made people didn’t want to accept it.

“People have a natural reaction to seek out information that counters that and reassures them that it’s not happening,” he said.

“I can understand negative reactions.”

Dr Corney said he commonly heard the people say they “don’t believe in climate change”.

“Climate change isn’t a matter of belief, it’s not a faith system,” he said.

“I have seen the evidence and the evidence is overwhelming and I accept that evidence.

“It’s not like a religion — if we could prove it’s not happening that would be the biggest step forward for anyone’s career and you’d be a hero.”

Dr Grose and Dr Lenton said scientists relished opportunities to prove each other wrong, but because they see the evidence first hand no scientist could be in denial.

“If one of us was to prove that climate change wasn’t real there’d be a Nobel Prize in that,” Dr Lenton said.

“We’ve all seen evidence and we all draw conclusions from that,” Dr Corney added.

Contributors observed that historical photos from their regions showed beaches and waterways were always changing over time.

Dr Grose said he accepted that sediment moved around, and beaches could look different as sediment was washed away and brought back in.

He said scientists used quality measurements over a long period of time.

“We’ve seen more than 20 centimetres of sea level rise over the past 100 years,” Dr Grose said.

He said it had accelerated in past few decades.

Dr Lenton said when CO2 levels go up, so does the temperature — but the sea level was different.

“Once we put heat into the ocean it takes many thousands of years for the heat to come out again.”