The Truth About Global Warming: ⑦ Future Damage Assessment

Published: Dec. 12, 2025, 5:37 a.m. UTC

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So, What About Polar Bears?

By the way, while in Japan they are sometimes called "shirokuma" (white bear), the correct name is Hokkyokuguma, or Polar Bear. As mentioned at the beginning, the association between polar bears and global warming plays a role in evoking emotional sympathy from people. Consequently, polar bears are often treated as campaign mascots for global warming awareness, and are frequently discussed based on impressions rather than facts. While there are various debates about the impacts and interpretations of global warming, let's first examine the case study that validates the "concerns" about polar bears.

Are polar bears really facing extinction? Let's first look at the main arguments on this point.

The Argument That Polar Bears Are Not Facing Extinction

There is an argument that polar bears are not declining but rather increasing, so there is no need to worry. For details, please refer to, for example, "The State of Polar Bears 2021 by Susan J. Crockford". This document shows the trend of estimated polar bear population from 1960 to 2021. We can confirm an increasing trend in population, partly due to the success of steady conservation efforts for polar bears.

polarbear_pop_ja

Looking at the graph above, we can certainly confirm that the population has increased significantly from 1960 to around 2020. Looking at this result alone, one might interpret it as follows: as a result of heightened environmental awareness related to global warming, conservation activities for polar bears received abundant funding, and the conservation efforts were successful. But is that the right interpretation?

In reality, to understand how this population increase came about, you need to read the literature in detail. Actually, the work of confirming polar bear numbers generally requires long-term fieldwork in the Arctic and is a difficult task, so without understanding the processes and assumptions by which the estimates were obtained, it is impossible to properly evaluate the figures obtained. Unfortunately, I cannot introduce those details here, but if you are interested, please read the above literature. In any case, the conclusion is as follows:

In fact, even with ice melting due to warming over the past few decades, polar bear numbers have been increasing. Therefore, there is no immediate concern about extinction. The reason why polar bear numbers are increasing is that warming is actually advantageous for polar bears.

The main food sources for polar bears are ringed seals, bearded seals, and other seals. As a result of warming, when summer sea ice decreases, ringed seals and bearded seals become healthier and their reproductive capacity increases. As a result, polar bears have abundant prey and their numbers increase. Also, while polar bears rarely eat terrestrial prey, they can hunt terrestrial reindeer, and in fact, polar bears have a fairly wide range of food choices. It has also been found that they have the ability to adapt to environmental changes, as they have recently been moving in groups to Russian territories and obtaining food "on land". The above graph is the result of facts obtained through steady accumulation of research, and there seems to be no need to seriously question those facts (although it would be desirable to have more data points).

However, the absence of immediate extinction concerns is only valid as long as past assumptions remain unchanged. On the other hand, since global warming is a discussion about cases where past assumptions change, it should be noted that this does not mean we can predict long-term future populations.

The Argument That Polar Bears Face Extinction Risk

There is an argument that polar bear survival is at risk in the long term. For example, there is a paper by Péter K. Molnár et al. from the University of Toronto titled "Fasting season length sets temporal limits for global polar bear persistence". This paper starts from the premise that polar bears need sea ice to capture their main food source, seals, and that if global warming and sea ice reduction continue, their habitat will decrease overall. Since there is a limit to the period polar bears can fast, as warming causes the number of ice-free days to gradually increase, the period when they cannot prey on seals extends, eventually exceeding the survival limit for polar bears. As a result, the paper shows that under high greenhouse gas emission scenarios, polar bear reproduction and survival will sharply decline by 2100, threatening the survival of the species.

Let me explain a bit about the part that says "polar bears need sea ice to capture seals." Many people have seen on National Geographic or TV the scene where white-colored polar bears use ice as camouflage to approach and prey on seals. However, on ice-free land, even if there are groups of seals on rocky shores or sandy beaches along the coastline, polar bears stand out too much and cannot approach seals. As a result of warming, even if many healthy seals breed in large numbers, it becomes game over if the method of catching them is cut off. Please consider this situation.

The left side of the figure below shows a moderate and stable greenhouse gas emission scenario (RCP4.5), and the right side shows a high emission scenario (RCP8.5). The vertical arrangement shows the names of regions where polar bears mainly inhabit. This chart visualizes how survival risk increases over time by region where polar bears are observed, with darker colors indicating gradually increasing risk. The risks are visualized separately for adult female survival, adult male survival, and cub recruitment risk.

polarbear_2100

Looking at these results, it appears that there is no significant manifestation of risk even under the high greenhouse gas emission scenario until around 2060. However, since warming takes effect through accumulation over time, it will be too late if we wait until around 2060 to say "polar bears are indeed in crisis." By the way, according to the above paper, if a mother bear with newborn cubs enters summer when the sea ice melts in a condition where she weighs 20% less than normal due to lack of food, the lower limit of the mother bear's fasting survival limit is 67 days (upper limit is 134 days). If this is exceeded, the mother bear will die. If the mother bear dies, naturally the cubs are also unlikely to survive.

To rephrase this in terms of sea ice presence or absence: the period from when the sea ice melts and they can no longer maintain footing to catch seals, until winter arrives and the ice becomes solid enough to catch seals again, must be within about three months. In the long term, seals will remain the main food source for polar bears. While there is a possibility of survival by obtaining other prey on land, in reality, the extent to which they can adapt to environmental changes remains unknown until it actually happens.

However, there is unfortunate historical evidence. During the Late Pleistocene (approximately 120,000 to 10,000 years ago), polar bears expanded their habitat south to the Baltic Sea, but with the subsequent Holocene warming and increased ice-free periods, they did not move to land and adapt, but simply disappeared from those regions.

As a cause of such occurrences, a scenario is envisioned where groups that choose to endure without moving to conserve energy for large-scale migration to land when entering fasting with insufficient food may lead to extinction because they cannot endure, even though they might have survived if they had given up on sea ice. In particular, mass migration of groups with newborn cubs would be extremely difficult.

Thus, while research on the future survival potential of polar bears has not yet produced sufficiently clear answers, isn't the situation that "specific scenarios for extinction are being narrowed down"? At the very least, there are no optimistic grounds sufficient to justify the claim that "there is no extinction risk."

IPCC Projections

Arctic Sea Ice Melting

Looking at IPCC predictions, even under moderate scenarios, by around 2070, all Arctic Ocean ice may melt completely in September. In other words, for polar bears, securing their main food source of seals would become extremely difficult. In this situation, the possibility of keeping the fasting period for mother bears with babies within three months is almost nonexistent. Considering that the lifespan of wild polar bears is about 15-18 years, the impact on extinction risk when the next generation cannot be raised would be enormous.

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Also, Declaration B.5 of the IPCC Sixth Assessment Report explains as follows:

Many changes due to past and future greenhouse gas emissions, particularly in the ocean, ice sheets, and global sea level, are irreversible for hundreds to thousands of years
In the long term, sea level will inevitably rise for hundreds to thousands of years and remain elevated for thousands of years due to continued deep ocean warming and ice sheet melting (high confidence). Over the next 2,000 years, global mean sea level will rise by approximately 2-3 m if warming is limited to 1.5°C, 2-6 m if limited to 2°C, and 19-22 m with 5°C warming, and will continue to rise for thousands of years thereafter (low confidence). These projections of global mean sea level rise over thousands of years are consistent with levels reconstructed from past warm climate periods. About 125,000 years ago, when global temperatures were very likely 0.5-1.5°C higher than 1850-1900, sea levels were likely 5-10 m higher than present, and about 3 million years ago, when global temperatures were 2.5-4°C higher, sea levels were very likely 5-25 m higher (medium confidence)

Impact of Climate Instability on People

Regarding regional climate instability, the IPCC Sixth Assessment Report explains, for example, as follows. I have excerpted some easily understandable passages:

B.2: Many changes in the climate system become larger in direct relation to increasing global warming. This includes increases in the frequency and intensity of extreme heat, marine heatwaves, heavy precipitation, and agricultural and ecological droughts in some regions, increases in the proportion of intense tropical cyclones, and reductions in Arctic sea ice, snow cover and permafrost
B.2.4: With further global warming, heavy precipitation will become more intense and more frequent in most regions with very high confidence. Globally, extreme daily precipitation is projected to intensify by about 7% for every 1°C of global warming (high confidence). The proportion of very intense tropical cyclones (Category 4-5) and peak wind speeds of the most intense tropical cyclones are projected to increase globally with further global warming (high confidence)
B.3: Continued global warming is projected to further intensify the global water cycle, including its variability, global monsoon precipitation, and the severity of wet and dry events
C.2.6: Cities intensify human-caused warming locally, and further urbanization with more frequent extreme heat will further increase heat wave severity (very high confidence). Urbanization also increases average precipitation and heavy precipitation over and/or downwind of cities (medium confidence), with resulting increases in runoff intensity (high confidence). In coastal cities, the probability of flooding increases due to more frequent extreme sea levels (from sea level rise and storm surge) and extreme rainfall or river flows (high confidence)

The figure below shows changes in annual average precipitation by temperature rise scenario, and in the case of a $$4°C$$ rise scenario, regions that become wetter and regions that become drier are shown to become very distinctly separated. When it rains, major floods occur; when it doesn't rain, major droughts occur, making extreme weather more likely.

rainfall

It may be difficult to feel you understand just from being given these results. Therefore, I will next explain a basic understanding of this mechanism.

Positive Feedback in the Atmosphere to Temperature Changes

Positive feedback refers to a state where, when there is a change from the current state, events progressively advance in the direction of that change. For example, Earth's temperature tends to receive stronger drive in the direction of change once it changes (positive feedback), and it is important to have a qualitative understanding of this mechanism. Specifically, that feedback is the following loop:

Atmospheric temperature rises ⇒ Sea ice melts ⇒ The mechanism (albedo) that reflected sunlight back into space decreases ⇒ The amount of solar energy absorbed and stored as heat by land and oceans increases ⇒ Atmospheric temperature rises

As a result of this cycle, regions with more ice currently are more susceptible to the effects of temperature rise. The same applies to the doldrums near the equator. The doldrums is an area near the equator with weak winds, sandwiched between the northeast trade winds of the Northern Hemisphere and the southeast trade winds of the Southern Hemisphere. This zone becomes a low-pressure zone due to rising air currents caused by strong solar radiation, and is also called the equatorial low-pressure zone, where thunderstorms and squalls are likely to occur.

1. Temperature rise ⇒ Increase in atmospheric saturated water vapor capacity (the atmosphere can hold more moisture)

2. Temperature rise ⇒ Expansion of temperature difference between ground surface, sea surface temperature and upper atmosphere ⇒ Strengthening of updrafts

3. (As a result of 1 and 2) ⇒ Moisture-laden air is cooled in the upper atmosphere by updrafts, generating large amounts of rain

When the above cycle is strengthened, regions that were already rainy receive even more rain. Dry regions such as subtropical high-pressure zones can be understood as a continuation of this. Subtropical high-pressure zones are formed when air that rose to the upper atmosphere due to updrafts generated at the equator accumulates around 30 degrees latitude due to the Coriolis effect and becomes a downdraft. Since downdrafts are hot and dry, deserts form on land located in subtropical high-pressure zones (such as the current Sahara Desert). Here, if more dry downdrafts blow, dryness further progresses.

With this level of understanding, you should be able to roughly interpret the IPCC's color-coded map of humid and arid regions due to temperature rise mentioned above. In other words, we can consider that the IPCC simulation results model such common-sense scenarios as rough scenarios.

Future Challenges Regarding Damage Assessment

While IPCC results are very important, because future predictions are extremely difficult, very difficult-to-understand expressions like the above declarations are used. Furthermore, more specific information about which regions will experience what level of problems is not described in detail by the IPCC. In other words, there is insufficient information to assess whether the land where you live will become uninhabitable in the future, whether it will be fairly serious, or whether there will actually be no significant impact.

Also, regarding polar bears, while the Arctic region is particularly affected by global warming, raising the possibility of extinction, information is also lacking about which animals in other regions are at risk and to what extent.

To raise the crisis awareness of the general public, researchers should definitely investigate such information. For example, information like "the area around the home you purchased with your life's investment will become uninhabitable in 50 years and turn into ruins" or "our ancestors have lived on this land for generations, but it will become uninhabitable within 100 years" is more likely to become a driving force for changing people's behavior.

At least, some of the current global warming skepticism in the world includes views such as "global warming is happening and droughts and heavy rains will increase in the future, but it won't cause problems for our daily lives. Those who make it sound like a major event are probably trying to make money from it." To properly address such arguments, we need to enhance information availability.