Bjorn Lomborg’s claims about polar bears, coral, and cold deaths ignore scientists’ predictions of climate-change-affected futures

The effects of climate change, caused by human greenhouse gas emissions, are manifold. Warming atmospheric temperatures lead to shrinking ice coverage in Earth’s poles, warmer water in Earth’s oceans, and hotter and more frequent extreme temperatures. Importantly, as the world grows warmer, those effects will also become more severe.

In a Wall Street Journal opinion piece, Bjorn Lomborg attempts to downplay some of these effects. Primarily linking to posts he has made on X (Twitter) since 2021, Lomborg claims that polar bear populations are actually rising, thanks to a reduction in hunting. He claims that data on coral coverage shows that the Great Barrier Reef is actually in good health. Finally, he claims that deaths from extreme heat have reduced.

Readers should be aware of Lomborg’s history of misleading claims that either downplay the effects of climate change or portray them as net positives. Indeed, much of Lomborg’s article repeats assertions, made both by himself and others, that Science Feedback has reviewed in the past. Likewise, in this review, we show that Lomborg’s claims oversimplify complex phenomena or lack important context. One of the most important misleading aspects of the article is that it attempts to refute what scientists have projected for the future (e.g. a decline in polar bear populations, threatened Great Barrier Reef, increased mortality due to heat) by arguing that it has not happened yet. We show below that science clearly forecasts that a warming climate will endanger both polar bears and coral reefs and put more humans at risk from extreme temperatures.

The data does not show that polar bear populations are increasing

Lomborg’s claims of prospering polar bears rely on incomplete data, as Science Feedback has addressed in a past review. Lomborg cites data from the IUCN SSN Polar Bear Specialist Group from 1981 to 2021 and compares it to unreliable 1960s-era estimates from other sources to purport that polar bear numbers have more than doubled between the 1960s and 2021. The Polar Bear Specialist Group tallies its numbers by combining regional counts of 19 different polar bear subpopulations, each located in a different region of the Arctic. But accurate polar bear counts do not exist for every region. Polar Bears International says that 10 of the 19 regions are currently too data-deficient to even discern if their respective polar bear populations are increasing or decreasing. 

So even today’s polar bear counts rely on guesswork, and those counts become even murkier the further we go into the past. Thea Bechsoft, a staff scientist at Polar Bears International, told AFP that polar bear population counts from before the mid-1980s are highly unreliable, meaning that we cannot use them to meaningfully assess how the polar bear population has changed between the 1960s and today.

Because scientists lack adequate data, they typically use other measures to judge polar bear health: most prominently, the number of sea-ice-free days¹. Polar bears use floating sea ice as platforms for hunting their prey, and polar bears fast when sea ice retreats north during the warm season. The less sea ice there is, the longer a polar bear’s habitat goes ice-free and the longer that bear must fast. We have visual evidence that Arctic sea ice is disappearing. Since satellite observations began in 1979, the area of Arctic sea ice in September (when sea ice is typically at a minimum) has shrunk by an average of 12.2% per decade. Scientific analyses have clearly linked this decline to warming Arctic temperatures thanks to greenhouse gas emissions².

So, we can’t say with any confidence that polar bears have increased in number. But can we say polar bears have benefitted from a decline in hunting? An international agreement banned most polar bear hunting in 1973, with exceptions for indigenous communities using traditional hunting methods. Research suggests that some populations affected by intensive hunting did recover after the 1973 ban. However, the same research indicates that any recovery was countered by the Arctic’s ebbing sea ice, which as we’ve seen is a direct consequence of climate change, and which decreases the Arctic’s carrying capacity for polar bears². 

Geoff York, senior director of research and policy at Polar Bears International who worked for 10 years as a biologist for the Polar Bear Research Program at the USGS, told Science Feedback:

Research has documented recovery from what was deemed overharvest at the time in regions like the Southern Beaufort and Barents Seas specifically. In the Southern Beaufort, that recovery has since been replaced by a 40% decline linked directly to sea ice habitat loss from warming³. In the Barents Sea, research suggests that recovery there may have stalled due to a declining carrying capacity from habitat loss and alteration driven by warming.

Note that neither the Southern Beaufort nor the Barents Sea populations (located north of Alaska and north of Norway, respectively) are considered data-deficient.

We see that polar bears are already threatened by the effects of climate change, and scientists predict the threat will only become more severe. In simulations conducted via the cutting-edge climate model CMIP6, the Arctic becomes effectively sea-ice-free in September by around 2060 in a high-emissions scenario (SSP5-8.5) and by around 2100 in a medium-emissions scenario corresponding to the world’s current emissions track (SSP2-4.5)⁴. CMIP6 simulations may even underestimate the rate of sea ice decline compared to observations, and studies that adjust CMIP6 to account for those observations predict sea-ice-free Arctic Septembers as early as around 2040 in both high- and medium-emissions scenarios⁵. Lomborg’s claim neglects any mention of these future trends.

Lomborg oversimplifies the Great Barrier Reef’s health

To argue that the Great Barrier Reef (GBR) is in good health, Lomborg cites data showing that coral coverage across the entire reef is at its highest point since measurements began in 1986. Lomborg’s choice of data is a poor reflection of the reef’s health, and he fails to account for how climate change will impact the GBR in the future.

It is important to remember that the GBR is very large: more than 2,300 kilometers (1,400 miles) from north to south, greater than the length of Italy. So, when Lomborg uses reef-wide data, he is doing the equivalent of gauging the weather of an entire region by using a single location average. Science Feedback contacted the Australian Institute of Marine Sciences (AIMS), which collects and publishes the hard coral coverage data that Lomborg used. The AIMS reef monitoring team stated:

[Lomborg’s] claim is not a misinterpretation of the data but is an oversimplification of a large complex system. A GBR-wide average of coral cover is too broad a spatial scope to summarize the condition of a reef system the size of a small country. Such summaries smooth over the nuances and variability of condition and status of regions within the GBR. Importantly, most disturbances which drive coral cover dynamics tend to occur at scales smaller than the entire GBR. For example, Cyclone Hamish in 2009 caused a large decline in coral cover in the southern region but left the northern and central regions intact; a GBR-wide average would have falsely indicated this decline occurring everywhere and diminished the magnitude of this decline. 

Additionally, as we have addressed in several different articles, it is true that the Great Barrier Reef has experienced several years of high hard coral coverage, but it is misleading to call this an indicator of long-term good health. Instead, the high hard coral coverage reflects the GBR’s recovery from past disruptions, such as coral bleaching events. For example, some of the Reef’s rapid growth in the early 2020s is the result of young and fast-growing Acropora corals spreading as the Reef recovers from major bleaching episodes in 2016, 2017, and 2020. However, the Reef will need 10 to 15 years in order to fully return to its pre-bleaching health and diversity of coral species after an episode.

The AIMS monitoring team also told Science Feedback:

Our long-term monitoring is showing that in the last 15 years, coral cover is going from its lowest lows to its highest highs – the variability is becoming much more erratic. While the increases in coral cover are encouraging showing the Reef’s capacity for recovery from the repeated shocks of disturbance events, these shocks are increasing in frequency and are more intense – future recovery is not guaranteed. This is the rollercoaster ride the Reef is facing at 1.1C of warming.

In fact, the data that Lomborg uses is not recent enough to include a major bleaching event that affected the entirety of the reef earlier this year. Coral bleaching often happens when a reef’s surrounding water temperature is warmer than normal. Indeed, bleaching events will only increase in frequency as the oceans warm in tandem with the atmosphere, leading to higher water temperatures and more frequent marine heat waves⁶. 

Under a high-emissions scenario (SSP3-7.0), the Great Barrier Reef will experience a severe bleaching event every year on average by 2080, with starker effects in the GBR’s south. Even under a low-emissions scenario (SSP1-2.6), the GBR will experience a severe bleaching event nearly every other year on average by 2080⁷. If bleaching events occur this frequently and this relentlessly, the reef will have hardly any time to recover.

Deaths from heat are in decline, but global warming is expected to reverse the trend

Finally, Lomborg cites data from two studies to claim that US deaths from cold temperatures vastly outnumber US deaths from heat⁸ and that, when adjusted for age, deaths from extreme heat have declined over the course of a decade⁹, thanks in part to cooling technologies like air conditioning. Again, however, Lomborg does not mention that these studies only represent current trends. Other studies project a rise in temperature-related deaths in future scenarios, particularly in certain parts of the world.

First, we should understand how these two studies work. Rather than individually counting deaths recorded from temperature-related causes like heatstroke or hypothermia, these studies compare mortality in a given location to that location’s daily temperatures over time, then analyze the number of excess deaths^8,9. This allows public health scholars to capture mortality related to factors like cardiovascular or respiratory diseases, which extreme temperatures can aggravate. The first study indicated that, in 13 countries on 5 continents between 1985 and 2012, around 7.3% of all deaths could be attributed to cold weather and 0.4% of all deaths could be attributed to hot weather⁸. The second study found that, across 43 countries, the number of heatwave-related excess deaths per population declined by 7.2% each decade between 1990 and 2019⁹.

Pierre Masselot, a statistician and environmental epidemiologist at the London School of Hygiene & Tropical Medicine, told Science Feedback: 

The specific figures are always subject to caution and uncertainties because they are the result of complex epidemiological modeling, but the evidence is now quite clear that there is a much higher mortality toll attributed to cold than to heat, and the biggest chunk comes from the so-called “moderate” cold…Regarding the temporal trends, they are also relatively clear that the risk of mortality related to heat has decreased, especially in the last 10 years.

Masselot, however, warns against using this data to make the misleading conclusion that climate change saves lives. In fact, in a 2021 New York Post article reviewed by Science Feedback, Lomborg claimed that climate change is saving several hundreds of thousands of lives per year by reducing the number of cold-related deaths. Neither the studies he cites nor other research support that conclusion, as we describe in our prior review. Additionally, a 2021 study in Nature Climate Change found that climate change can be blamed for 37% of warm-season heat-related deaths between 1991 and 2018¹⁰.

Furthermore, even when considering the spread of adaptations like air conditioning, it is especially important to note that the trend of decreased mortality from heat is not guaranteed in the future. “Even with decreased vulnerability — and we don’t know how far this can improve — if the years get hotter and hotter under climate change, it is very much possible the trend reverses in the future,” Masselot told Science Feedback.

In fact, Masselot said there is reason to believe the trend has already begun to reverse. A study published in August 2024 in Nature Medicine analyzed heat-related deaths in Europe between 2015 and 2023. The authors found that 2022 and 2023 saw the highest and second-highest heat-related death counts of any year in their timeframe, and their study did account for adaptations like air conditioning¹¹. The summers of both years brought heat waves and record-breaking temperatures to Europe. Such extremes are expected to become even more frequent on a warming planet¹².

Moving into the future, it is important to recognize that as the entire planet warms, different climates will experience different temperature shifts. Regions with warmer climates today, for example, will be more vulnerable to heat-related dangers. In a 2017 study published in The Lancet, the same research team behind the two studies cited by Lomborg projected how both cold- and heat-related deaths would evolve under a range of climate change scenarios in nine regions around the world. Their projections showed more temperature-related deaths under a medium-emissions scenario (SSP2-4.5) in South America, Central and Southern Europe, and Southeast Asia. In a high-emissions scenario (SSP4-8.5), all those regions saw even starker total increases, as did North and Central America¹³. In the mentioned regions, a reduction in cold-related deaths did not balance an even larger increase in heat-related deaths.

Additionally, while it may seem logical to conclude that fewer people will die from cold-related causes in warmer climes, a warming planet may actually exacerbate the risk of cold-related deaths. Another study published in The Lancet in August 2024 projected temperature-related mortality in Europe under 1.5°C, 2°C, 3°C, and 4°C of global warming since pre-industrial times (compared to 1°C of warming today). The authors noted that cold-related deaths actually slightly rose in the 1.5°C and 2°C scenarios, even while heat-related deaths also rose. Cold-related deaths did decrease in the 3°C and 4°C scenarios, but again not by enough to balance out even more dramatic rises in heat-related deaths — which nearly quadrupled under 4C of warming¹⁴.

By ignoring these possibilities, Lomborg presents temperature-related mortality as an insignificant, reversible phenomenon. However, this is a misleading claim that diminishes the very real threat posed by extreme temperatures in a warming world — particularly in warmer regions of the planet closer to the Equator.

Conclusion

In this opinion piece, Lomborg acknowledges climate change as real while downplaying the severity of its effects. The article could allow a reader to come away with several misleading implications: for example, that polar bear populations and the Great Barrier Reef are both in good ecological health, and that deaths from extreme heat will continue to decline. As we have shown, Lomborg excluded important context, especially omitting to explain to his audience that these climate change effects are forecasted by scientists to become more severe in the future. Simply because something has not yet happened does not mean it will not happen.

References:

1. Molnár et al. (2020) Fasting season length sets temporal limits for global polar bear persistence. Nature Climate Change.
2. Amstrup and Bitz. (2023) Unlock the Endangered Species Act to address GHG emissions. Science.
3. Bromaghin et al. (2015) Polar bear population dynamics in the southern Beaufort Sea during a period of sea ice decline. Ecological Applications.
4. Intergovernmental Panel on Climate Change. (2021). Future Global Climate: Scenario-Based Projections and Near-Term Information. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change.
5. Kim et al. (2023) Observationally-constrained projections of an ice-free Arctic even under a low emission scenario. Nature Communications.
6. Hughes et al. (2017) Global warming and recurrent mass bleaching of corals. Nature.
7. McWhorter et al. (2021) The importance of 1.5°C warming for the Great Barrier Reef. Global Change Biology. 
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9. Zhao et al. (2024) Global, regional, and national burden of heatwave-related mortality from 1990 to 2019: A three-stage modelling study. PLOS Medicine.
10. Vicedo-Cabrera et al. (2021) The burden of heat-related mortality attributable to recent human-induced climate change. Nature Climate Change. 
11. Gallo et al. (2024) Heat-related mortality in Europe during 2023 and the role of adaptation in protecting health. Nature Medicine.
12. Thompson et al. (2023) The most at-risk regions in the world for high-impact heatwaves. Nature Communications.
13. Gasparrini et al. (2017) Projections of temperature-related excess mortality under climate change scenarios. The Lancet Planetary Health.
14. García-León et al. (2024) Temperature-related mortality burden and projected change in 1368 European regions: a modelling study. The Lancet Public Health.