Photo/Website of University of Hamburg

The huge impact of global climate change has once again sounded alarm for all mankind. On July 4 World Meteorological Organization declared the return of El Niño. The National Oceanic and Atmospheric Administration data shows that the global average temperature for two consecutive days (July 3 and July 4) broke the record.

Extreme weather has occurred frequently this year. In the Mediterranean, for example, the end of April was the hottest on record; In early June, the temperature in Siberia reached nearly 38℃.

Among the many consequences of climate change, the widespread melting of sea ice in the Antarctic, Arctic, and North Atlantic is much discussed. Antarctic sea ice extent has continued to hit record lows due to a sharp rise in sea surface temperatures, and Arctic sea ice has continued to be extremely low this year. In early June, a paper published in Nature Communications suggested it was too late to save summer Arctic sea ice, and scientists said they needed to prepare for the increase in extreme weather in the Northern Hemisphere.

Dirk Notz, professor of sea ice and cryosphere and deputy director of the Institute of Oceanography, at the University of Hamburg in Germany, called for a global shift in the energy system from fossil-based to renewable energy based. "Stopping greenhouse gas emissions is by far the least costly way to stop global warming, rather than paying for dire consequences for decades and centuries to come."

NBD: Some claim that the effects of climate change (e.x. the aforementioned phenomena ) will be the "gray rhinos" of our time. Do you agree with this claim and why?

Dirk Notz: I agree with this characterization: Climate change will have severe consequences in every part of the Earth. We humans are changing the face of this planet for many millennia to come, and have become the strongest geological force for changes in the Earth System. The consequences will have primarily negative impacts for many generations to come, yet we do very little to change our emission of greenhouse gases. To stop global warming, we must reduce greenhouse gas emissions to net zero. In reality, however, we had a new record in CO2 emissions in 2022, despite all calls for reductions of greenhouse gas emissions.

NBD: Your team's research shows that even if greenhouse gas emissions are sharply reduced, the Arctic will be ice-free in September in the coming decades. Is the melting of Arctic ice really (and sadly) irreversible? Will the melted ice re-condense into the same volume of ice during the winter?

Dirk Notz: Our study was concerned with the relatively thin (1-2 meters) sea ice that covers the Arctic Ocean. In the seasonal cycle, it has its smallest extent in September, at the end of summer. Over the past thirty years, we have melted already about three-quarters of the summer sea ice volume that we had in the Arctic in the 1990s. It seems extremely unlikely that we will stop global warming fast enough to rescue the remaining quarter. We, therefore, expect the first ice-free September at some point between 2030 to 2050. With strong efforts to reduce greenhouse gas emissions, we can still limit the duration of the ice-free period, and we can prevent ice loss to happen every year. In winter, however, the open ocean will still freeze and form sea ice for many decades to come.

NBD: If the ice in the Antarctic, North Atlantic, and Arctic continues melting at the current pace, what would it mean for the global ecosystem, biodiversity, and the entire human being? 

Dirk Notz: The Arctic sea-ice cover carries a unique ecosystem, ranging from polar bears to small algae that form at the bottom of the ice every spring and summer. This ecosystem will change drastically with the disappearing sea ice. Already now, we see new species invading the Arctic, as the water there gets warmer and ice-free periods become longer and longer. They push existing species aside, and we expect a loss of species that are unique to the Arctic over the coming decades. For us humans, the loss of the Arctic summer sea ice is yet another sign of the incredible power that we have over this planet: we can wipe out a complete landscape. This also means that we carry great responsibility. I do not think that we do justice to this responsibility at the moment, but instead ignore it...

NBD: Now that reducing greenhouse gas emissions is so urgent, why aren't governments taking enough actions and policies? How should countries cooperate to engage and prioritize this issue?

Dirk Notz: Stopping global warming is an incredibly difficult task: We must change the energy system from a fossil-based one to a renewable-based one all around this globe. All countries must cooperate on this, to share the burden and help each other with technology, money, and insight, to keep this transition just and fair. This is more the case given the historical responsibility that arises from past greenhouse gas emissions. We must understand that humanity as a whole and our planet, really are under threat, and we must somehow manage to put national interests aside and realize that these national interests are at risk in every country if we don’t jointly on stopping global warming. I think it’d be great if we could see climate change as a chance to work together to keep this planet as beautiful and amazing as it was when we were born

NBD: Is (sharply) reducing greenhouse gas emissions enough for humans to tackle climate change? Should governments target zeroing greenhouse gas emissions ahead of schedule?

Dirk Notz: To stop global warming, we must reduce and finally stop emitting greenhouse gases. The slower we do so, the warmer the climate will become. And with every bit of global warming, with every tenth of a degree, the damage done by climate change will increase. It is by far the cheapest option to stop global warming as soon as possible, rather than paying for the consequences in the decades and centuries to come.