Q. There has been much emphasis on the impact climate change will have on our natural environment, but perhaps less on what it will mean for our health. Do you feel there's a lack of awareness about climate change being a major health issue?
A. If we ask ourselves, what are the really bad outcomes from climate change that we would want to avoid? most people would put serious illness and injury high on the list.
Yet it is true that climate change is seldom described as a health issue.
I think this is because the most significant threats to human from climate change are indirect - through pathways such as population displacement, food shortages, and changing patterns of disease vectors.
Also, it is hard for those of us who live in high income countries with robust housing to imagine that we are really and truly vulnerable to climate variations.
So attention tends to fall on the direct and immediate effects of a hotter, more energetic climate - sea level rise, floods, effects on forests and crops.
Q. Under different projections, what are some of the health impacts we might expect with the environmental shifts which would result from climate change, such as fewer cold days in winter, heat waves and extreme weather events?
A. More frequent and more severe extreme heat is the "finger print" of climate change.
The 2010 heat wave in Russia, for instance, which caused roughly 11,000 deaths - we know the risk of such extreme events is five times greater than would be expected under a stationary climate.
In July this year temperatures around the Persian Gulf were for the first time close to the upper limits that humans can survive, without air conditioning.
If emissions follow a business as usual track, by early next century, my colleague Tord Kjellstrom has estimated, it is more likely than not that people in at-risk regions like northern India will encounter these levels of lethal heat every year.
In the tropics heat already limits people's capacity to work outdoors. On a business as usual scenario, we are heading to a situation where it is actually physically impossible to carry out heavy work without artificial cooling.
Q. With an average temperature several degrees warmer, what potential would this pose for the spread to New Zealand of diseases more suited to tropical climes?
A. If average temperatures rose by a couple of degrees in New Zealand, this would certainly make conditions easier for mosquitoes and other vectors that spread disease.
The major threats are illnesses caused by insect-spread viruses like dengue fever and Ross River fever. It is unlikely that local transmission of malaria would be an issue, even with moderate warming.
Q. How is climate change already having a health impact in New Zealand?
A. It is likely, in my view, that climate change is already having effects on health in New Zealand.
In this country storms, floods, droughts and heat all have effects on health, and we know conditions are changing with rising levels of carbon dioxide and other greenhouse gases.
But it is difficult to pin point exactly what illnesses are caused by climate change. The reason is that the rate of change is slower in New Zealand than almost any other country.
Rising temperatures have been buffered by the large amount of ocean around us, and we are south of the tropical storm belt.
The effects of climate change, health and other kinds of impacts are clearer in other countries in our region, such as Australia, and some of the Pacific island states, for instance.
Q. Globally, what widespread impacts on human health is climate change projected to bring, in terms of hunger, disease and disaster risk?
A. In the next 20 to 30 years high temperatures and changes in rainfall patterns are expected to reduce food production in tropical areas, and make crop yields more variable.
Those who will suffer most are those populations who are already vulnerable to hunger.
But if global heating continues, then there will be immense challenges to food security world-wide. There are many diseases sensitive to climate. Water-borne infections like cholera, for instance.
And climate change is expected to act as a risk multiplier, so sanitation and safe water supplies will be even more important in the future than at present.
It is projected that mosquito-borne diseases like malaria and dengue will be more difficult to control in many places, as a result of climate differences.
Q. How significant do you expect the health impacts from increased migration, and reduced social stability, would be alone?
A. Climate change may trigger large movements of people, due to prolonged drought, food shortages, flooding and sea level rise, with many associated health problems.
These include mental health issues, infectious diseases, and all the conditions associated with poverty.
The present flood of people from Syria gives an indication of how challenging it is to maintain social stability in the face of rapid, involuntary migration.
Q. Are there any positives for health that might come with the impacts of climate change? And how negligible might they be in contrast with the negative outcomes?
A. There will be positives for health, for some people, due to climate change.
Fewer extreme cold conditions, for instance, may make a difference in some places. In some tropical countries it is projected to be too hot for some infectious diseases, such as malaria.
It is likely that food production will be boosted, for a time, in northern countries like Canada.
My judgement is that these positive effects will not persist, if warming continues through this century and beyond, and will be exceeded world-wide by the negative effects on human health.
Q. And what are the health benefits that can arise from efforts to combat climate change, be they burning fewer fossil fuels, cycling instead of driving, or simply eating less red meat?
A. Wise climate choices can achieve substantial health benefits, rapidly. A shift to clean energy sources, better balanced transport systems, a less carbon-intensive diet: these are all good examples of win-win interventions.
If we could move 5 per cent of short urban trips from cars to bikes, for example, we have estimated that New Zealand could save 20 million litres of fuel a year, and there would be roughly 100 fewer premature deaths a year due to conditions like diabetes and heart disease.
Q. This year, researchers said the last 50 years of gains in development and global health could be undone by climate change, calling it a "medical emergencY". As it stands, how equipped is the world's health system today to meet this crisis, and is it already preparing?
A. It is patchy. Some countries are taking the threats of climate change very seriously, and gearing up their health systems.
After Hurricane Sandy for instance, New York City has spent millions of dollars on relocating communities, better early warning systems and more effective emergency medical care.
But many other countries don't have the resources, and struggle to deal with day to day health emergencies, let alone what lies ahead.
This is true for many Pacific island countries for instance.
Q. In this context, how important will the climate talks in Paris be to the medical community?
A. COP21 is very important for the medical community. It is the best opportunity yet to get off the "business as usual" trajectory of emissions.
It will be a huge challenge to stay within 2 degrees of warming by 2100, which is likely to bring with it very serious health threats.
But without significant action in Paris, the world is more likely than not to experience 4C of warming, on average, by the end of the century. I fear this rate of change would bring with it health problems that may be unmanageable.