For much of the last half of the previous century, we worried most about a nuclear holocaust. While that remains a worry, the world has survived for almost seventy five years without a nuclear explosion as an act of war.

While living in fear of a nuclear cloud, there have been major developments in improving the quality of human life. Medicine provided new treatments that seemed to make many old diseases virtually disappear. As technology made life easier, it seemed that average life spans will keep going up and people all over the world will live better. Of course, we cannot live forever so as we get older, new medical problems appear to take us to the other side.

However, as a new century progresses, humanity is confronting new threats and some old ones are coming back in new clothes. Sadly, most of these threats are results, directly or indirectly, of human activity. These threats can roughly be divided into two categories. There are those that directly affect humans and those that alter the environment we live in and thus pose a danger to us.

Almost all of these will require a full discussion as the year goes on but I will at least list some of them along with a brief introduction.

About the personal threats that have emerged, the more important of these are new sources of infection that might not have been important in the past. An example of this is a fungus called Candida Auris. This has emerged in the last decade as the cause of virulent infections that are often resistant to most antifungal medicines.

Interestingly, there are four types of this fungus that have been identified and all come from different parts of the world. One reason suggested for the drug resistance of this fungus is the anti-fungal crop sprays that are used and have allowed this particular fungus to become resistant to the antifungal drugs.

Then we have the very much in the news, the ‘new’ coronavirus. How far this one will go remains to be seen. Along with this we have had other new viruses that have emerged over the last many years and caused major disease and bad outcomes.

The next group of problems is old and well-known infections that we thought were under control but now bacteria causing these have started to become resistant to drugs used to treat them effectively in the past. Most important for Pakistan among these are typhoid and tuberculosis.

The next group of problems deals with environmental pollution. When we think of a clean environment we think of pure mountain air and pristine mountain streams. Sadly most of us do not live in such places and if we did the air would no longer be pure and the water pristine.

We have always had dust that contains not just the basic minerals in it but also a lot more. There are bacteria and fungi and sadly dried waste from animals and other humans. Over time we as humans have developed the ability to protect ourselves from most of these things we breathe along with air.

In human history the first deliberate air pollution started with the discovery of fire. With the ability to cook food and have light came smoke. And rather than the forest fire this smoke became a part of our homes, starting with the cave onwards. In time the human body did develop the ability to handle some of the things we breathe in that get absorbed into the blood stream.

Then we have the very much in the news, the ‘new’ coronavirus. How far this one will go remains to be seen. Along with this we have had other new viruses that have emerged over the last many years and caused major disease and bad outcomes.

But then came the industrial revolution and suddenly it was not just smoky fires at home but also an entire environment full of smoke from factories and automobiles and other forms of transportation. So now we have a mixture of pollutants in the air that easily overwhelm the ability of the body to handle these poisons in the air. And add to this pollution what a billion or so people inhale in addition — cigarette smoke. And all this smoke included a lot of gasses — more about those later.

The other form of pollution is that of water. Almost all surface water and rivers become contaminated when they become accessible to humans. And the contamination is not just human waste but also industrial waste. Many rivers not only contain dangerous chemicals that can harm humans but are also a source of bacteria that are resistant to antibiotics.

The other form of environmental pollution is from what are called greenhouse gasses. These gasses form a sort of blanket around the earth that keeps the warmth derived from the sun in the earth atmosphere. It is because of this warmth that the earth has been hospitable to all life including our own.

Unfortunately, as we burn more fossil fuels, we produce more of these gasses, the major one being carbon dioxide. As these gasses accumulate in the atmosphere, we are getting too much of a good thing and the atmosphere is starting to warm up a lot more. And the deforestation that is going on the world over makes this heat trapping even worse.

This ‘global’ warming is starting to produce climate change. Here an important point worth emphasising. Weather is what happens over a day or a week but climate is what happens over a much longer period of time. The one important result that we are probably starting to see as a result of this change in climate is that the summers are becoming hotter, the winters colder and the monsoons wetter.

And if this warming continues, eventually we in our part of the world will see melting glaciers; and changing living environment due to loss of river water that we get from the melting glaciers. In other parts of the world this warming will produce other results. Sadly none of these will be good for humanity.

The world we live in has undergone periods of catastrophic climate change due to natural disasters. The most well-known is when a meteorite the size of the island of Manhattan hit the earth in the area of the Gulf of Mexico some sixty six million years ago. This produced changes in the climate that led to the extinction of the dinosaurs and gave a chance to the mammals to flourish.

It does seem that we would not be here but for that meteorite. That was nature’s doing, but what is happening now is occurring as a result of human activity. And unless humankind does something to prevent further global warming, earth might just become too hot for humans to live.

It is unlikely that all forms of life will disappear if the earth warms up some more but for humans it might become a bit too warm. However, we must also accept the fact that human ingenuity can and will work on keeping this world habitable for most of us.

Until that point of no return is reached, perhaps we should also worry about the dengue virus and inhaling too much of the polluted air or at least not make it worse by inhaling cigarette smoke.

The writer has served as Professor and  Chairman, Department of Cardiac Surgery, King Edward Medical  University