Saturday, November 28, 2009

HOW SWINE FLU OUTBREAK EMERGED

HOW SWINE FLU OUTBREAK EMERGED


Flu viruses in different species
Flu viruses mutate over time causing small changes to proteins on their surface called antigens. If the immune system has met a particular strain of the virus before, it is likely to have some immunity; but if the antigens are new to the immune system, it will be weakened.
Flu virus mutation
The influenza A virus can mutate in two different ways; antigenic drift, in which existing antigens are subtly altered, and antigenic shift, in which two or more strains combine. Antigenic drift causes slight flu mutations year on year, from which humans have partial, but not complete, immunity. By contrast, the new strain of H1N1 appears to have originated via antigenic shift in Mexican pigs
Antigenic shift in pigs
The name "swine flu" is a slight misnomer as it is believed pigs acted as a mixing pot for several flu strains, containing genetic material from pigs, birds and humans. Most humans have never been exposed to some of the antigens involved in the new strain of flu, giving it the potential to cause a pandemic.
Virus transmission to humans
The new virus has made the jump from pigs to humans and has demonstrated it can also pass from human to human. This is why it is demanding so much attention from health authorities. The virus passes from human to human like other types of flu, either through coughing, sneezing, or by touching infected surfaces, although little is known about how the virus acts on humans.

Q&A: Advice about swine flu

Q&A: Advice about swine flu


Swine flu has spread across the world since emerging in Mexico and is now officially the first flu pandemic for 40 years. Experts fear millions of people will be infected.

What is swine flu and what are the symptoms?

SWINE FLU SYMPTOMS
Human body with internal organs
Typical symptoms: sudden fever (38C or above) and sudden cough
Other symptoms include:
1. Tiredness and chills
2. Headache, sore throat, runny nose and sneezing

3. Stomach upset, loss of appetite, diarrhoea

4. Aching muscles, limb or joint pain

Source: NHS

Swine flu is a respiratory disease, caused by a strain of the influenza type A virus known as H1N1.

H1N1 is the same strain which causes seasonal outbreaks of flu in humans on a regular basis.

But this latest version is different: it contains genetic material that is typically found in strains of the virus that affect humans, birds and swine.

Although the strain may have originated in pigs, it is now a wholly human disease.

It can be spread from person to person by coughing and sneezing.

Symptoms of swine flu in humans appear to be similar to those produced by standard, seasonal flu - fever, cough, sore throat, body aches and chills. Some people with the virus have also reported nausea and diarrhoea.

However, many people who get flu show no symptoms at all.

Health experts say this could happen in half of all cases and with swine flu an analysis has shown that for children one in four of those infected may not fall ill.

What are the risks of the flu?

Experts have wrestled with the question ever since the pandemic emerged.

The problem is that for most people it is mild - about 98% recover without the need for any hospital treatment.

But doctors have found it very hard to predict who will develop complications, hence it has been dubbed a "Jekyll and Hyde" virus.

A fifth of the people who have died have been previously healthy individuals without any health conditions.

Nonetheless, certain groups are known to be at higher risk.

Pregnant women are between three to four times more likely to get seriously ill.

Young children also have higher rates of hospitalisation - although this could be partly because doctors are quicker to admit them.

Should I have the vaccine if offered it?

The vaccination programme is well under way.

Nearly 14m people, including NHS workers, people with health problems and pregnant women, will be offered the jab by Christmas. Healthy children under the age of five are also due to start getting it.

But already polls suggest people are worried about whether to get vaccinated.

The government says that getting immunised is the best way to protect yourself against flu.

However, its experts recognise that people are jumpy about vaccines and have said it is very much a personal decision.

People who are suspicious of vaccines often talk about the risk of complications.

One of the most common which is mentioned in association with flu vaccines is Guillain-Barré syndrome (GBS), a rare disorder in which a person's own immune system damages the nerve cells, causing muscle weakness and sometimes paralysis.

Most of the evidence suggests vaccines do not increase the risk, however there is research to indicate that getting flu increases it seven-fold.

Another allegation sometimes made is that being given the vaccine could actually give you flu.

Doctors are adamant this is not the case - the two vaccines being used in the UK do not contain the live virus.

As for deaths, the World Health Organization has been monitoring this and while a handful of people have died after being given the vaccine, officials have ruled out any link to the jab.

Why has the UK been more affected than other countries?

The UK has a comprehensive flu surveillance system, hence more cases may be identified in the UK than in other countries with less comprehensive monitoring services.

Also, the spread of the infection in the early stages was linked to flights out of Mexico.

FLU PANDEMICS

1918: The Spanish flu pandemic remains the most devastating outbreak of modern times. Caused by a form of the H1N1 strain of flu, it is estimated that up to 40% of the world's population were infected, and more than 50 million people died, with young adults particularly badly affected

1957: Asian flu killed two million people. Caused by a human form of the virus, H2N2, combining with a mutated strain found in wild ducks. The impact of the pandemic was minimised by rapid action by health authorities, who identified the virus, and made vaccine available speedily. The elderly were particularly vulnerable

1968: An outbreak first detected in Hong Kong, and caused by a strain known as H3N2, killed up to one million people globally, with those over 65 most likely to die

With Mexico being a popular tourist destination for British tourists, Britain was one of the first countries alongside the US and Canada to start seeing cases.

As the UK was affected earlier than some other countries the infection spread to a higher number of people at the start of the pandemic.

However, as the British summer progressed, cases fell, while southern hemisphere countries saw rises as they went through their winters.

More recently cases have started going up again in the UK, but other countries, such as France, also have high rates.

What should I do if I think I have it?

Anyone with flu-like symptoms who suspects they might have the swine flu virus are being advised to stay at home and contact the National Flu Service on 0800 1 513 100 or via the internet at www.direct.gov.uk/pandemicflu

The service allows sufferers to get access to anti-flu drugs without the need to consult a GP.

However, those with underlying health conditions, pregnant women and parents of children under one are still being advised to contact a doctor.

The GP route is also open to anyone who does not want to use the service.

In the initial phase of the outbreak, lab testing was done to diagnose the flu but this is no longer happening routinely.

How is it treated?

Two drugs commonly used to treat flu, Tamiflu and Relenza, are effective at treating infection, reducing the length of the illness and cutting the chances that people will have serious complications.

Use of these drugs may also make it less likely that infected people will pass the virus on to others.

However, the drugs must be administered at an early stage to be effective.

Researchers have also questioned whether the drugs are helpful in children aged between one and 12, saying the risk of side effects might outweigh any benefits.

But the Department of Health maintains a "safety-first approach" of offering antivirals to everyone remains a sensible and responsible way forward.

It said it would keep the policy under review.

Where can I get further advice?

Further information and advice on swine flu can be found at websites of leading health and research organisations around the world. The World Health Organisation gives background information on the virus.

The UK's government services website is carrying regularly updated health and travel information. The Health Protection Agency advises the public about what to do if returning from an affected area. NHS Choices outlines how swine flu is different from other flu.

The European Centre for Disease Prevention and Control is another good source of information.

The US government's Centers for Disease Control and Prevention is counting the number of cases in the US.

You can also track spread of swine flu reports using unofficial sources. Google is mapping search term data as an indicator of flu activity both across the US down to state level and in Mexico. Healthmaps maps viruses using news reports. Social media guide Mashable lists a range of ways to track the virus .

Information and links to useful websites are being shared on Twitter, the micro-blogging service, while social networking website Facebook is tracking swine flu discussion amongst users.

Further questions from our readers have been answered by a UK-based expert.

And the BBC's medical correspondent, Fergus Walsh, is filing regular entries on his blog on H1N1.

Fergus On Flu

Fergus On Flu
http://news.bbc.co.uk

Death rates and mutations

I don't want to end the week on an alarming note, and - let's face it - there's been enough alarmist reporting about H1N1 swine flu.

But I would like to draw your attention to a couple of issues which many of you are likely to pick up elsewhere on the web or perhaps in the papers.

The first is a big jump in the global death toll. The World Health Organization said the number of deaths was up around 1,000 on a week ago, reaching at least 7,826 worldwide since the H1N1 virus emerged in April. That should neither surprise nor alarm you. We are now getting into the peak flu season. Seasonal flu kills several hundred thousand very elderly and frail people each year. The difference with swine flu is that the majority of deaths are in the under-65s.

On a more positive note, the WHO said that the epidemic may have peaked in parts of the northern hemisphere. That seems to be the case in the UK and in the United States, which has had several weeks of falling levels of flu.

Secondly, I have picked up via BBC Monitoring that two patients in France, in different hospitals, have died from mutated H1N1 swine flu. (For those who don't know, the BBC monitoring service is based in Caversham in Reading; it listens to news broadcasts from around the world and provides accurate translations.)

The monitoring translation of La Chaine Info Television went like this:

French newsreader: "The health authorities dreaded this. The H1N1 virus is in the process of mutating. The phenomenon reported in Norway has also been detected in France in two deceased patients who were not related in any way and who were in hospitals in two different cities. This mutation could increase the virus's ability to affect certain airways, as well as the lungs."

Read like that, it seems pretty scary, and it is certainly not good news that mutations are occurring. But, as has been pointed out by me and by many of the wise men and women who post comments here, mutations are what we should expect with flu. Flu is an RNA virus in which genetic replication is pretty poor and which makes lots of mistakes. It's the reason that flu viruses drift and the reason we need a new flu jab every winter.

The mutations reported in France have been seen in Norway and in several other countries, and the WHO put out some very clear advice on this recently.

The French mutation has been found in two cities, but we need to know a lot more about it before becoming unduly alarmed. The patients may have been immuno-compromised, making them more susceptible to mutated viruses, and we don't have any evidence that mutated strains are spreading in the wider community.

To sum up, mutation and deaths are sadly unavoidable when it comes to H1N1 swine flu. But this pandemic is still reassuringly mild for the vast vast majority of those infected.

GPs urged to go 'full throttle' in accelerating vaccination

Around one million people in England are now estimated to have been vaccinated against swine flu.

Across the UK, 10 million doses of the vaccine have been distributed to GPs and hospitals.

That one million figure refers to those in the initial priority groups, such as those with chronic asthma, heart and other organ disease, immune problems and pregnant women.

Clearly there is still a long way to go. There are nine million people in the priority groups in England, and around 11.5 million across the UK. Then add to that the three million or more under fives who will be offered the jab after that.

Professor David Salisbury, Director of Immunisation at the Department of Health said he hoped GPs would now be able to accelerate the vaccination process:

"All GPs have now had some vaccine and we are now at the stage of re-stocking them and so the brakes can come off to some extent. We'd like to get the priority groups vaccinated before Christmas, and there will be enough vaccine to do that. GPs don't want to call in patients if they are unsure there have enough vaccine, but now they know they have it in the fridge they can go full throttle."

Professor Salisbury said he wanted doctors to get through the priority groups as quickly as possible so that they could move on to immunising children under five.

Carers for the elderly and disabled will also be entitled to receive the swine flu jab once the initial priority groups have been cleared.

I hope this answers some of the questions many of you have raised about the roll-out of the vaccine.

There are no figures yet for the uptake of vaccine among more than two million front-line health workers.

But Ian Dalton, National Director for Flu Resilience said that "informal conversations" had shown promising levels of uptake. He gave some examples:

• West Midlands Ambulance Service has offered the jab to around 1,000 front line staff and 70% have accepted.
• Guy's and St Thomas' Hospitals have received 2,000 doses and used 1,500 already.
• They have also immunised 4,000 staff against seasonal flu, double the number last year.

So how much swine flu is there in Britain at present? Estimated figures from across the UK suggest cases are falling very slightly but the number of deaths is rising sharply.

Indeed the past week has seen the biggest single rise in deaths since the pandemic began.

UK deaths to date related to H1N1 swine flu: 245
163 England
13 Northern Ireland
46 Scotland
23 Wales

Why are deaths rising if cases are falling? Firstly, remember that weekly estimates for the number of cases of swine flu are probably wildly out (but are useful for showing trends over time).

The latest weekly estimate for England was 46,000 cases of swine flu with a cumulative total of 760,000. But since the Health Protection Agency now reckons that one in five children may have had swine flu, that cumulative figure maybe just a tenth of the real total (and that's just my guess).

I've discussed this apparent contradiction about falling cases and rising death rates earlier this month - something that has been seen in other countries.

It's important to note that there is no evidence that the H1N1 swine flu virus is mutating into something more deadly.

Finally a few graphs - very useful for showing trends. My thanks to the Department of Health and the RCGP for supplying the data:

Influenza-like illness England and Wales

You can see that the rate of flu is now about average for this time of year but well below the peak we saw in July.

Hospitalised patients in England

This is a snapshot of the number of patients in hospital in England with suspected swine flu related illness as of 25 November. It's always worth showing this because it's a reminder that while flu is mild for most, for a small minority it can be very serious.

Confirmed deaths related to swine flu by week

This is the first time I've seen this. It reveals the death toll from swine flu, in England from week to week. You can see that the rate has risen throughout November.

Useful resources:

Detailed UK weekly epidemiology update
Swine flu figures for Northern Ireland
Swine flu figures for Scotland
Swine flu figures for Wales

Up to a third of children in some areas have been infected

It's been one of the big questions of this pandemic. Just how many of us in Britain have actually had swine flu?

Knowing that would be incredibly useful, as the bigger the proportion infected, the further we are into this pandemic and the less likely there will be a further sting in its tail.

The Health Protection Agency (HPA) has done blood tests of hundreds of children and parents connected to early school outbreaks.

With one school in south west England they tested around 500 people. They found that although around one in 10 children fell ill, three to five times as many got infected and developed antibodies.

After analysing this and other data relating to the number of children being seen by GPs, the HPA has now come up with these interesting estimates:

• Up to one third of children in swine flu hotspots (such as England and the West Midlands) have already been infected with the H1N1 virus.
• Across the UK up to one in five children has had had swine flu.
• About half of those who get infected show no symptoms.

This is all very reassuring. Professor Maria Zambon from the HPA said:

"We didn't get the pandemic that we planned for and you might say that we've been lobbed a soft ball. There hasn't been high case mortality, the virus is sensitive to drugs, and we've been able to make vaccine and roll it out. I am incredibly grateful that we are not dealing with a pandemic of H5 (bird flu)."

Professor Zambon said the virus had had a relatively low impact on older adults and that was probably explained by pre-existing immunity. The HPA has these estimates:

• For those aged over 50 up to four in 10 people have pre-existing protective antibodies to the H1N1 pandemic virus.
• If you are under 50 it falls to around one in 10 of the population.

The professor, who is an acknowledged world expert on flu, did utter a few words of caution. "Influenza is full of mystery and intrigue. It has lots of twists and turns" and she predicted that mutations of the swine flu virus should be expected. She also pointed out that there could still be a substantial outbreak of seasonal flu over winter.

Jump in number of global swine flu deaths

Jump in number of global swine flu deaths


Mexico City commuters on the metro
The virus was first recorded in Mexico

The global number of swine flu deaths has jumped by more than 1,000 in a week, latest figures from the World Health Organization (WHO) show.

At least 7,826 people are now known to have died following infection with the H1N1 virus since it first emerged in Mexico in April.

Europe saw an 85% increase in the week, with the total number of deaths rising from at least 350 to at least 650.

However, in most cases the virus continues to produce mild symptoms.

If every mutation is reported out there it would be like reporting changes in the weather
Keiji Fukuda
WHO special adviser on pandemic influenza

An overwhelming majority of patients usually recover, even without medical treatment, within a week.

The biggest rise in deaths was recorded in the Americas, where the death toll rose to 5,360 - a rise of 554 cases in one week.

Health authorities in Norway and France have each recorded two fatalities from a mutated strain of H1N1.

China, Japan, Norway, Ukraine and the US have also recorded cases of people being infected with a mutated strain.

Uncertainty

French health officials confirmed that two patients infected by a mutation that was also recently detected in Norway had died in two different cities in France.

SWINE FLU SYMPTOMS
Human body with internal organs
1. High temperature, tiredness and lowered immunity
2. Headache, runny nose and sneezing
3. Sore throat
4. Shortness of breath
5. Loss of appetite, vomiting and diarrhoea
6. Aching muscles, limb and joint pain
Source: NHS

"This mutation could increase the ability of the virus to affect the respiratory tracts and, in particular, the lung tissue," said a statement from the government's Health Surveillance Institute.

The French institute added that, in the case of one of the patients who died, the mutation was accompanied by another mutation known to confer resistance to the main drug being used to treat swine flu, which is sold under the brand name Tamiflu.

It was the first drug-resistant strain found in France among the 1,200 strains experts have analysed here, it said.

Speaking on Thursday, Keiji Fukuda, the WHO's special adviser on pandemic influenza, said that conclusions had still to be drawn about the reported mutations.

"The question is whether these mutations suggest that there is a fundamental change going on in viruses out there - whether there's a turn for the worse in terms of severity," he said.

"The answer right now is that we are not sure."

Dr Fukuda noted that mutations were common in influenza viruses.

"If every mutation is reported out there it would be like reporting changes in the weather," he said.

"What we're trying to do when we see reports of mutations is to identify if these mutations are leading to any kinds of changes in the clinical picture - do they cause more severe or less severe disease?

"Also we're trying to see if these viruses are increasing out there as that would suggest a change in epidemiology."

In his latest survey of swine flu developments, the WHO notes that many countries have stopped counting individual cases of swine flu, particularly of milder illness, and the case count is likely to be significantly lower than the actual number of cases that have occurred.

Cell discovery clues to body clock and beating jet lag

Cell discovery clues to body clock and beating jet lag


By Dave Lee
Health Check, BBC World Service

A man yawns
The discovery could hold the key to solving body clock mysteries

New discoveries into how the body clock works could provide clues to help combat jet lag, research suggests.

A University of Manchester team studied special cells which they say play an important role in regulating a person's body clock.

The cells had been thought to be inactive during the day - but their research found the opposite is true.

It is hoped the findings may also pave the way to combating sleep disorders triggered by body clock malfunctions.

Professor Hugh Piggins, an expert in neuroscience at the university, said the research will allow a new approach to being able to tune our daily clock.

Two cells

The Manchester research turns on its head the idea that the brain keeps the body clock on track by firing more cells during daylight and very few during the night.

There's a lot of interest in the pharmaceutical industry, obviously, to try to develop chemical treatments to reset your daily clock
Professor Hugh Piggins

"The traditional model said the clock and the brain communicated to the rest of the brain via the number of electrical impulses that the brain cells were producing," Prof Piggins told the BBC World Service's Health Check programme.

"These impulses would travel around the brain, telling it what time of day it is.

"What we've found is in fact that there are at least two types of cells in this part of the brain."

These brain cells behave unlike any other cell seen so far, and contain a key gene - per1 - which allows them to sustain unusually high levels of "excitability".

The cells becoming so "excited" that they seem quiet or even dead; but then later they calm down, recover and become normally active again.

It is this activity which tells the human body when to be awake.

Sleep dysfunction

HEALTH CHECK
Health Check
Health Check is the weekly health programme broadcast from the BBC World Service
It is broadcast on Monday at 1032GMT and repeated at 1532GMT, 2032GMT and on Tuesday at 0132GMT
It is also available as a podcast

Prof Piggins added: "There's a lot of interest in the pharmaceutical industry, obviously, to try to develop chemical treatments to reset your daily clock to help counteract things like jetlag.

"Or, perhaps more importantly, different kind of sleep disorders for which dysfunctions in this clock are often involved."

This study marks the first time these "quiet" cells have been studied.

"This may mean that elsewhere in the brain there are cells like this that can also survive these very unusual conditions."

Climate change around the world

Climate change around the world


World leaders at the G8 summit in Italy are negotiating a deal to limit the effects of climate change. Click on the buttons and words above to find out more about the impact of global warming.

AFRICA

Some regions are likely to experience water shortages. Coupled with increasing demand, this is likely to result in large increases in the number of people at risk of water scarcity. It is likely to affect livelihoods, the report by the International Panel on Climate Change says.

Projected reductions in the area suitable for growing crops, and in the length of the growing season, are likely to produce an increased risk of hunger. In some countries, yields from rain-fed agriculture could be reduced by up to 50% by 2020.

Rising sea levels threaten large cities. Degradation of coral reefs and mangroves is likely, with impacts on local fisheries and tourism.

Rising temperatures, coupled with over-fishing, will decrease the supply of fish from large lakes, with important impacts on food supplies.

ASIA

Glacier melting in the Himalayas is virtually certain to disrupt water supplies within the next 20 to 30 years. Floods and rock avalanches are virtually certain to increase. Heavily-populated coastal regions, including the deltas of rivers such as the Ganges and Mekong, are likely to be at risk of increased flooding.

Economic development is likely to be impacted by the combination of climatic change, urbanisation, and rapid economic and population growth.

Forecast changes in temperature and rainfall are likely to reduce crop yields overall, increasing the risk of hunger.

The presence of lethal diarrhoeal diseases associated with floods and droughts is expected to rise in East, South and Southeast Asia and rises in coastal water temperature could exacerbate cholera in South Asia.

AUSTRALIA AND NEW ZEALAND

Ongoing water shortages, notably in southern and eastern Australia, are likely to get worse by 2030.

Ecologically important regions such as the Great Barrier Reef and Kakadu National Park are likely to lose a significant part of their wildlife before then, by 2020.

Some coastal communities are very likely to see an increased risk of coastal storms and flooding.

Temperature rises of 1C-2C are likely to bring benefits to cooler areas, such as New Zealand, in the form of longer growing seasons and reduced energy demand. Greater warming is likely to bring a net negative impact - such as increased risk of drought and fire.

EUROPE

Nearly all European regions are expected to be negatively affected by some future impacts of climate change.

Central and Eastern European countries could face less summer rainfall, causing higher water stress. Health risks due to heat waves are expected to increase. Forest productivity is expected to fall and the frequency of peatland fires to increase.

Southern European countries are very likely to see reduced water supplies, lower crop production, more wildfires and health impacts from increased heatwaves.

Northern countries are likely to benefit from increased crop yields, forest productivity, and food supplies from the North Atlantic. By 2020, most areas of Europe are likely to see an increased flood risk.

LATIN AMERICA

Increasing temperatures and decreases in soil water in the eastern Amazon region would lead to replacement of tropical forest by savannah. Species extinctions are likely.

Drier areas are likely to see salinisation and desertification of agricultural land, with falling crop yields and livestock productivity reducing food security. However, soybean yields are likely to increase in temperate zones.

Sea level rise is very likely to bring flooding to low-lying regions such as the coast of El Salvador, Guyana and the Rio de la Plata estuary. Increasing sea temperatures are likely to impact coral reefs and south-east Pacific fish stocks.

Changes in rainfall patterns and the disappearance of glaciers are projected to significantly affect water availability for human consumption, agriculture and energy generation.

NORTH AMERICA

Warming in western mountains is very likely to reduce snowpack, bringing more floods in winter and reduced water supplies in summer.

Increases in problems with pests, diseases and forest fires are likely.

Cities with a history of heat waves are likely to experience many more, with potential health impacts, especially for the elderly.

Rising sea levels, severe weather and storm surges, combined with population growth in coastal areas, are very likely to increase economic losses.

POLAR REGIONS: ARCTIC AND ANTARCTICA

Reductions are likely in the thickness and extent of glaciers and ice sheets, and the extent of sea ice and permafrost.

The depth of summer permafrost melting is likely to increase.

Changes to natural ecosystems are likely to impact migrating birds, mammals and higher predators adversely. Specific ecosystems and habitats are expected to be vulnerable, as climatic barriers to species invasions are lowered.

There are virtually certain to be both negative and positive effects on Arctic peoples. Detrimental impacts would include those on infrastructure and traditional indigenous ways of life while beneficial effects would include reduced heating costs and more navigable northern sea routes.

SMALL ISLANDS

Sea level rise is likely to worsen floods, storm surges and coastal erosion, with impacts on the socio-economic wellbeing of island communities.

Beach erosion and coral bleaching are likely to reduce tourism.

There is strong evidence that water resources in small islands are likely to be seriously compromised.

Increased invasion by non-native species is likely.

WATER

The supply of water is very likely to increase at higher latitudes and in some wet tropics, including populous areas in east and southeast Asia. It is very likely to decrease over much of the mid-latitudes and dry tropics, which are presently water-stressed areas.

Drought-affected areas will likely increase. Instances of extreme rainfall are likely to increase in frequency and intensity, raising the risk of floods. Increases in the frequency and severity of floods and droughts will have implications on sustainable development.

Water volumes stored in glaciers and snow cover are very likely to decline, reducing summer and autumn flows in regions where more than one sixth of the world population currently live.

ECOSYSTEMS

Many ecosystems are likely to be challenged beyond their capacity to adapt over the course of the century by an unprecedented combination of climate change, associated disturbances such as wildfires, and other aspects of modern-day global change.

In the second half of this century, ecosystems on land are likely to become a net source of carbon rather than a net absorber. This extra carbon will amplify climate change.

Roughly 20-30% of species are likely to be at high risk of irreversible extinction if the global average temperature rises by 1.5-2.5C beyond 1990 levels. For increases in global average temperature exceeding 1.5-2.5C, there are very likely to be major changes in ecosystems which will adversely effect the environmental goods and services which humans use.

FOOD

Crop yields are likely to increase at higher latitudes for global average temperature increases of up to 1-3C (depending on the crop), and then decrease beyond that. This is even after allowing for effects of CO2 fertilisation.

At lower latitudes, especially the seasonally dry tropics, crop yield potential is likely to decrease for even small global temperature increases, which would increase risk of hunger.

Global agricultural production potential is likely to increase with increases in global average temperature up to about 3C, but above this it is very likely to decrease.

Increased frequency of droughts and floods would affect local production negatively, especially in subsistence sectors at low latitudes.

COASTS

Coasts are very likely to be exposed to increasing risks due to climate change and sea level rise, and the effect will be exacerbated by increasing human-induced pressures on coastal areas.

It is likely that corals will experience a major decline due to increased bleaching and mortality due to rising seawater temperatures. Salt marshes and mangroves will also be negatively affected by sea-level rise.

Many millions more people are expected to be flooded every year due to sea-level rise by the 2080s, especially in densely populated and low-lying settlements which already face other challenges such as tropical storms or local coastal subsidence. The numbers affected will be largest in the mega-deltas of Asia, but small islands face the highest relative increase in risk.

INDUSTRY

The benefits and costs of climate change for industry, settlement, and society will vary widely by location and scale. Some of the effects in temperate and polar regions will be positive, and others elsewhere will be negative. Generally, a higher degree of warming is more likely to bring negative consequences.

The most vulnerable industries, settlements and societies are those in coastal and river flood plains, those whose economies are closely linked with climate-sensitive resources, and those in areas prone to extreme weather events, especially where rapid urbanisation is occurring.

Poor communities can be especially vulnerable because they tend to be concentrated in relatively high-risk areas, have more limited coping capacities, and can be more dependent on climate-sensitive resources such as local water and food supplies. Where extreme weather events become more intense, the economic costs of those events will increase, and these increases are likely to be substantial in the areas most directly affected.

HEALTH

Projected climate change is likely to affect millions of people, particularly those with low capacity to adapt, through increases in malnutrition and consequent disorders.

This will have implications for child growth and development; increased deaths, disease and injury due to heat waves, floods, storms, fires and droughts, the altered burden of water-related diseases; the increased frequency of cardio-respiratory diseases due to higher concentrations of ground level ozone, and the movement of some infectious disease carriers into new regions. vectors.

Climate change is likely to have some mixed effects, such as the expansion and contraction of the range of malaria in different regions. In some places, climate change is likely to bring some benefits to health such as fewer deaths from cold exposure.

IPCC definitions of probability of occurrence

Virtually certain: more than 99%
Extremely likely: more than 95%
Very likely: more than 90%
Likely: more than 66%
More likely than not: more than 50%
Very unlikely: less than 10%
Extremely unlikely: less than 5%

Copenhagen: What's your solution?

Copenhagen: What's your solution?



Smoke rises over the skyline of Jilin, China

If you had the microphone at the Copenhagen climate summit, what would you say?

What is your message to world leaders on global warming?

BBC News would like you to send us your message for Copenhagen.

The best video messages we receive will be featured in a special televised debate on BBC News, at the climax of the conference.

Last chance

The UN Climate Change Conference begins in Copenhagen, Denmark, on December 7.

Example of a video message - Children send their messages to Barack Obama

Some say it is our last chance to save the world from runaway climate change.

Many hope that world leaders will agree significant cuts in greenhouse gas emissions; and compensation for countries suffering from global warming.

But talks so far have been slow, with key nations cagey to commit. There are fears that no firm action will be agreed.

• Are you worried about climate change?

• What deal would you strike in Copenhagen?

• Who should cut their emissions? By how much? And how should they make these cuts?

• How would you improve the negotiation process?

Send us your comments in video

Life in 2050

How will climate change affect you in future?

The blue marble

Is it already affecting you now?

Perhaps you are farmer whose crops are vulnerable.

Or you may live in a coastal area at risk of flooding.

You may be an oil worker, or a coal miner whose job is threatened.

Whatever you do, we'd like to hear from you.

Tell us:

• Why does climate change matter to you?

• How much are you personally willing to adapt, to live more sustainably?

• Are you prepared to change the way you travel, the food you eat, or to have fewer children?

• Would you pay more taxes - to invest in green energy and compensate countries hurt by climate change?