Polar bears may struggle to produce milk for their cubs as climate change melts sea ice

During their time onshore, polar bear mothers may risk their survival by continuing to nurse when food is not available. (Shutterstock) Louise Archer, University of Toronto

When sea ice melts, polar bears must move onto land for several months without access to food. This fasting period is challenging for all bears, but particularly for polar bear mothers who are nursing cubs.

Our research, published in Marine Ecology Progress Series, found that polar bear lactation is negatively affected by increased time spent on land when sea ice melts.

Impaired lactation has likely played a role in the recent decline of several polar bear populations. This research also indicates how polar bear families might be impacted in the future by continued sea-ice loss caused by climate warming.

Challenges of rearing cubs

While sea ice might appear as a vast and perhaps vacant ecosystem, the frozen Arctic waters provide an essential platform for polar bears to hunt energy-rich seals — the bread and butter of their diet.

Sea ice is a dynamic environment that can vary through time and in different regions of the Arctic. Polar bears in Canada’s western Hudson Bay area experience seasonal sea ice, which melts in the warmer summer months, forcing the polar bears to move onto land until cooler winter temperatures cause the sea ice to refreeze.

On shore, polar bears often remain in a fasting state, using their body stores of fat for fuel. (Shutterstock)

While on shore, hunting opportunities are rare and polar bears generally spend their time in a fasting state. Polar bears rely on their immense body fat stores to fuel them during these leaner months, with some individuals measuring almost 50 per cent body fat when they come onshore in early summer.

While on land, polar bears can lose around a kilogram of body mass per day, so making it to the end of the ice-free season requires them to carefully manage their energy. For most polar bears, this means reducing activity levels and conserving energy until the sea ice returns and seal hunting can resume.

Females with cubs must also factor in the additional burden of lactation. Polar bears produce high-energy milk, which — at up to 35 per cent fat — is like whipping cream. This high-fat milk allows cubs to grow quickly, increasing from just 600 grams at birth to well over 100 kilograms by the time they are around two-and-a-half years old and leave their mothers to become independent.

During the onshore fasting period, polar bear mothers face a difficult trade-off: Stop lactating and risk the health of her growing cubs or continue nursing and risk her own survival as her energy reserves are depleted.

Polar bear cubs remain with their mothers for up to two-and-a-half years. (Shutterstock)

Moderating lactation

Although lactation is important to both mothers and cubs, studies on polar bear lactation are relatively rare.

To better understand how females manage their lactation investment, our research team revisited a data set of polar bear milk samples collected in the late 1980s and early 1990s from polar bears on land during the ice-free period.

We estimated how long each polar bear mom had been fasting based on annual sea-ice breakup dates and found that the energy content of their milk declined the more days spent onshore. Some bears had stopped producing milk entirely. Both milk energy content and lactation probability were negatively related to the mother’s body condition, meaning females in poor body condition had to prioritize their own energetic needs over their cubs.

The bears who reduced their investment in lactation benefited by using up less of their body reserves, meaning they could fast for longer. Yet the cubs who received lower energy milk grew more slowly than offspring of females that maintained their lactation effort. In the long term, this may reduce cub survival and, ultimately, negatively affect population dynamics.

Climate change and population declines

After around three months on land, the probability of a female with cubs lactating was 53 per cent. This dropped to 35 per cent for a female with yearlings (older cubs from the previous year).

The data in our study were collected around three decades ago. Since then, climate warming has meant that the ice-free season in western Hudson Bay has been extending by around seven days per decade. Polar bears are now regularly forced to spend more than four months on land.

As the ice-free season has increased and polar bears must go for longer without food, their average body condition has declined. The ability of female polar bears to nurse their cubs has probably also become increasingly impaired.

This may have contributed to the 50 per cent decline in the population size of the western Hudson Bay population over the last four decades, and is likely to contribute to further declines if climate warming and sea-ice declines continue as projected without mitigation.

This research adds another piece to our understanding of polar bear resilience to climate change. Without action to halt climate warming and sea-ice loss, survival of cubs will be at risk across the Arctic.

Louise Archer, Postdoctoral Fellow, Biological Sciences, University of Toronto

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Read More........→October 09, 2023

We are poised to pass 1.5℃ of global warming – world leaders offer 4 ways to manage this dangerous time

Marcus E Jones, Shutterstock Jonathan Symons, Macquarie University

For three decades, the goal of international climate negotiations has been to avoid “dangerous” warming above 1.5℃. With warming to date standing at around 1.2℃, we haven’t quite reached the zone we labelled dangerous and pledged to avoid.

But recent scientific assessments suggest we’re on the brink of passing that milestone. Within this decade, global annual temperatures will likely exceed 1.5°C above the pre-industrial average for at least one year. This threshold was already briefly passed for the month of July 2023 during the Northern summer. The question is, how do we manage this period of “overshoot” and bring temperatures back down? The goal will be to restore a more habitable climate, as fast as possible. Today an independent group of global leaders released a major report. The Climate Overshoot Commission offers guidance at this crucial time. So far the report’s call for an immediate moratorium on “solar radiation management” (deflecting the sun’s rays to reduce warming) has attracted the most attention. But the details of other recommendations deserve closer inspection.  How can we respond to climate overshoot? Historically, climate policies have focused on mitigation (reducing greenhouse gas emissions). More recently, adaptation has gained prominence. But the climate overshoot report identifies at least four different kinds of responses to warming above 1.5℃, 

• 1. cut emissions to mitigate warming
• 2. adapt to the changing climate 
• 4. remove carbon that is already in the atmosphere or ocean, 
• 5. explore intervening to limit warming by intentionally reflecting a fraction of sunlight into space. 

The commission’s task was to examine how all possible responses might best be combined. Their report was written by 12 global leaders – including former presidents of Niger, Kiribati and Mexico – who worked alongside a youth panel and a team of scientific advisers. The four-step plan to reining in warming Not surprisingly, the commission argues our central task is mitigation. Transitioning away from fossil fuels remains the first priority. But reaching net zero emissions is just the first step. The commission argues developed countries like Australia should go further and aim for net-negative emissions. Why net-negative? In the short term, drawing down carbon can create space for the least industrialised countries to fight poverty while transitioning to clean energy. In the longer term, the whole global economy must achieve net-negative emissions if the planet is to return to our current “safe” climatic zone. The second step is adaptation. Only a few decades ago former United States Vice President Al Gore branded adapting to climate change a “lazy cop-out”. Today we have no choice but to adapt to changing conditions. However, adaptation is expensive – whether it is developing new crop varieties or rebuilding coastal infrastructure. Since the poorest communities who are most vulnerable to climate harms have the least capacity to adapt, the commission recommends international assistance for locally controlled, context-specific strategies. As a third step, the commission agrees with scientific assessments that carbon dioxide “will need to be removed from the air on a significant scale and stored securely” if we are to avoid permanent overshoot beyond 1.5℃ warming. But how to achieve large-scale permanent, carbon removal? Some environmental activists support natural solutions such as planting trees but oppose industrial methods that seek to store carbon in inorganic form such as carbon capture and storage underground. The commission agrees the organic/inorganic distinction is important. However, it points out while forests bring many benefits, carbon stored in ecosystems is often re-released – for example, in forest fires. The commission worries many carbon removal approaches are phoney, impermanent or have adverse social and environmental impacts. However, instead of ruling out technologies on ideological grounds, it recommends research and regulation to ensure only socially beneficial and high-integrity forms of carbon removal are scaled up. The fourth step – “solar radiation management” – refers to techniques that aim to reduce climate harms caused by reflecting some of the Sun’s energy into space. No-one likes the idea of solar radiation management. But no-one likes getting vaccinated either – our gut reactions don’t provide a fool-proof guide to whether an intervention is a worth considering. Should we trust our guts on this one? While climate models suggest solar radiation management could reduce climate harms, we don’t yet properly understand associated risks. The commission approaches this topic with caution. On the one hand, it recommends an immediate “moratorium on the deployment of solar radiation modification and large-scale outdoor experiments” and rejects the idea that deployment is now inevitable. On the other hand, it recommends increased support for research, international dialogue on governance, and periodic global scientific reviews. Time to examine intervention in the climate system? The idea we can avoid dangerous warming completely seems increasingly quaint. Like baggy jeans, the boy band NSYNC and the iPod shuffle, it reminds us of a more innocent era. Yet, Australia’s climate debate often seems stuck in this era. The widespread hope we “still have time” means we are not yet discussing the merits of more interventionist responses to the climate crisis. However, there’s increasing reason to be sceptical incremental measures will be sufficient. We may soon be forced to move beyond the non-interventionist, conservation paradigm. Whether or not its recommendations are taken up, the Climate Overshoot Commission’s work shows how the international community has failed to avert dangerous climate change. Reckoning with the consequences of this failure will dominate public policy for decades to come. This new report takes us a step forward. Jonathan Symons, Senior Lecturer, Macquarie School of Social Sciences, Macquarie University This article is republished from The Conversation under a Creative Commons license. Read the original article.

Read More........→September 18, 2023