How will global warming affect polar bears?
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What the science says...
Polar bears are in danger of extinction as well as many other species.
Polar bears are found in the Arctic circle and surrounding land masses. There are 19 recognised subpopulations, and estimates place their numbers at about 20,000 to 25,000. Polar bears are classed as vulnerable by the World Conservation Union (IUCN) and listed as a threatened species under the US Endangered Species Act. Yet some claim that polar bear numbers have increased since the 1950s and are now stable. So what is the situation for this species?
First of all, a few points need to be made about polar bear numbers:
- Nobody really knows how many bears there were in the 1950s and 1960s. Estimates then were based on anecdotal evidence provided by hunters or explorers and not by scientific surveys.
- Polar bears are affected by several factors, including hunting, pollution and oil extraction. Most notably, hunting, particularly following the introduction of snowmobiles, airplanes and ice breakers, led to a huge decline in certain subpopulations. The introduction of the International Agreement on the Conservation of Polar Bears in 1973, which restricted or even banned hunting in some circumstances, consequently resulted in an increase in polar bear numbers.
- Not all subpopulations are affected to the same degree by climate change, and while some subpopulations are well studied, for others there is insufficient data to make broad statements about current and past numbers.
With this caveat in mind, what do the figures actually say? According to a 2009 report by the IUCN Polar Bear Specialist Group, of the 19 recognised subpopulations of polar bears, 8 are in decline, 1 is increasing, 3 are stable and 7 don’t have enough data to draw any conclusions. Figure 1 below compares the data for 2005 and 2009.
Figure 1: Subpopulation status of polar bears for 2005 and 2009 (Source: Polar Bear Specialist Group)
Both habitat degradation and over-harvesting are responsible for the decline in some subpopulations. To understand why the IUCN and US Endangered Species Act consider polar bears to be at risk, it is important to look at how rising temperatures are likely to affect their habitat in the future. Polar bears are highly specialised mammals which rely heavily on sea ice for food and other aspects of their life cycle. Satellite data show that Arctic sea ice has been decreasing for the past 30 years, and projections show that this trend will continue as temperatures carry on rising. The changes in sea ice affect polar bears in several ways:
- The early retreat of summer sea ice means that bears have less time to hunt and therefore less time to build up fat reserves.
- The fragmentation and reduction in sea ice has several impacts. It forces the bears to swim longer distances, using up some of their fat reserves. It also reduces the number of seals, which are the bears’ main source of food, and impedes travelling and den making. And it also forces the bears to spend more time on land, with increased interactions with humans potentially leading to higher mortality.
To get an idea of the potential impacts of future climate change on polar bears, we can look at subpopulations found at the bears’ southern range, where habitat changes have been most noticeable so far. A good example is the western Hudson Bay subpopulation, which is one of the best studied. Here, ice floe break-up is taking place earlier than 30 years ago, effectively reducing the feeding period by about three weeks. As a result, the average weight of female polar bears has dropped by about 21% between 1980 and 2004, and the population declined by 22% between 1987 and 2004. In Alaska, there is evidence of increased cub mortality caused by a decline in sea ice.
In conclusion, the reason polar bears have been classed as threatened comes from the impacts of future climate change on the bears’ habitat. Current analysis of subpopulations where data is sufficient clearly shows that those subpopulations are mainly in decline. Further habitat degradation will increase the threats to polar bears.
Basic rebuttal written by Anne-Marie Blackburn
Update July 2015:
Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial
A further website of interest is from WWF.
Last updated on 22 July 2017 by pattimer. View Archives
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A thesis statement or hypothesis is essentially what makes an essay what it is. This one statement, found in an essay’s introduction, tells a reader what the essay is about and what the writer’s main argument or research findings are. Because this sentence states the purpose of the essay itself, it should be clear and concise and provide the writer’s concrete view of the particular subject. Writing a thesis statement that clearly outlines your stance on the topic and that is easy to understand differentiates a strong essay from a weak one. In this article, what makes a good thesis will be explained. We also provide some thesis statement examples to show you what works.
A Thesis Statement Should be Arguable
A good thesis statement can be debated and, therefore, can be backed up by research to persuade others that the hypothesis is correct or the best solution to a problem. You want the reader of your essay to agree with whatever you have argued, so stating facts does not make a good thesis or a good essay. The point of research is to further knowledge of a particular subject. Take a look at this thesis statement example that is simple but arguable:
Saving endangered species, like the polar bear, should be the responsibility of all countries.
There are people who would argue that it is not up to the entire world to save the polar bear but that it is the responsibility of the countries in which polar bears are found. This statement is easily debatable.
A Thesis Statement Should be Focused
Writing a focused thesis statement will not only keep your writing on track and help you avoid an overwhelming amount of research but will also allow you to create a solid argument. Every hypothesis must be supported by evidence and research. You do not want to make so broad a statement that you need a wide range of evidence to support it. Focus your statement on a specific area of your topic, and narrow your research to just this area.
The disappearance of suitable climates in which woolly mammoths could live likely resulted in the extinction of the species.
The thesis statement example given here is focused on a specific aspect that likely contributed to the extinction of the woolly mammoth—climate change. Researching evidence on one aspect of your topic can strengthen the final argument.
A Thesis Statement Should Reflect the Type of Essay being Written
The way you’ll go about writing a thesis statement will depend on the type of essay you need to write. A thesis for a book review will be worded differently than a thesis for a research proposal. Each version outlines the main purpose of the essay itself. Below are thesis statement examples for a variety of essay types.
A book or journal review thesis is a statement of your critical evaluation of the book
In The Lord of the Rings, J.R.R. Tolkien explores the theme of friendship through the loyalty and respect displayed between many of the main characters, such as Frodo and Sam, Gimli and Legolas, and Merry and Pippin.
A position or argumentative essay thesis is a statement of your position and why you adhere to it
University graduates in the 21st century cannot find valuable work because of the state of the economy and because many workers of the baby boomer generation refuse to retire.
A comparative essay thesis is a statement of your main argument and the main points of your comparison
Dogs often make better pets than cats because they can be easily trained and are more emotionally responsive.
A research paper thesis is a statement of your main claim relating to a topic or problem
Because of a greater sense of community and cultural involvement, people who live in the city experience a higher quality of life than people who live in rural areas.
A research proposal thesis is a statement of what you believe to be the main claim about a topic or problem
Evidence indicates that children who learn an instrument frequently go on to work in creative fields as adults.
Once you have a solid understanding of your research topic, writing a thesis statement should be relatively simple. Having your thesis statement planned out before you start your essay will allow you to focus your writing and help you create a strong argument. Once you have compiled all your research and know what you want to say in your essay, try writing out a few versions of your thesis statement, keeping in mind that it must be arguable, focused, and appropriate for the type of essay you’re writing.
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