Do you remember the oppressive heat of the dry season? The heat that, here in Singapore, saw people become anxious as the water in the Linggiu Reservoir in Johor dropped to levels never seen before.

The rains washed away those concerns, but the heatwave, while it lasted, no doubt caused some to think about climate change.

Whether or not the record temperatures were directly linked with greenhouse gas emissions, most scientists agree that climate change will make extreme weather more likely.

And climate change is critical to the future being considered right now at the four-day World Cities Summit being held in Singapore, starting today. It is one of the world's biggest challenges: ever more people on the planet, and rising standards of living, generating more demand for energy, against the need to reduce greenhouse gas emissions. And cities are at the heart of the solution.

The global population is growing: from more than seven billion today, to an estimated 10 billion by 2050. And as the number of people swells, we expect the growth of cities to accelerate.

Half of the human beings on the planet already live in cities. By 2050, the proportion is on track to be around 70 per cent, with half of this growth in Asia alone.

Today cities consume two-thirds of world energy. By 2040 we can expect cities to be using almost 80 per cent.

Even with heroic efficiency efforts, the amount of energy the world is consuming by the end of the century is likely to double compared to today.

Yet how do we halt the accumulation of greenhouse gases like carbon dioxide in the atmosphere?

The Shell Scenarios team models possible futures and has just published its latest supplement, A Better Life With A Healthy Planet: Pathways To Net Zero Emissions.

In it we can see a possible path - challenging though it may be - to a world where emissions of carbon dioxide are at net zero levels. That means the emissions that remain are offset, or captured and stored below ground. This is not a target for Shell - it is something the world must achieve.

Cities, and how we plan them, will be central to achieving this. They have a huge opportunity to become more energy-efficient: through building standards; by using waste heat from power generation to warm homes; by encouraging high-density living to reduce travel and encourage smaller electric or hydrogen- powered cars; by building high- capacity public transport systems.

The evolving energy mix will be vital, too. Natural gas, for example, produces half the carbon dioxide and one-tenth of the air pollution of coal when burnt for power.

Gas power stations also partner well with renewables, providing reliable electricity when there is no sun or wind.

But adding carbon capture and storage (CCS) technology to power stations and industrial complexes will be critical to reduce emissions enough to reach net zero.

Renewables will, of course, continue to grow rapidly as part of the mix, but mainly produce electricity.

Today, electricity accounts for less than one-fifth of the total energy used in the world. For renewables to have a major impact, our scenario shows the share of electricity in the energy mix will need to grow to at least 50 per cent.

This means people must meet the costs of, for example, electric or hydrogen-electric cars. Households and businesses not supplied with waste heat must be warmed with electricity. Food processing and light manufacturing must also go electric.

Yet even with all this change, greenhouse gas emissions will continue to enter the atmosphere for the foreseeable future.

The production of chemicals used in so many of the things we take for granted will continue to rely on oil and gas. Where very high temperatures or dense energy storage are required - such as in the manufacture of iron, steel and cement, or in heavy freight and air transport - we will almost certainly see the continued use of hydrocarbon fuels.

There will also be regions that switch to low-carbon energy at different speeds, for political, economic or demographic reasons.

Continuing emissions will have to be offset. We can plant forests and use agricultural practices that raise the carbon content of the soil, such as ploughing partly burnt biomass into fields. We can also burn biomass for power, coupled with CCS. Industrial plants can suck carbon dioxide from the atmosphere. Using CCS can make sure it never goes back.

Whether in cities or beyond, none of this will be easy. But all of it is possible. If the world starts work right now.

• Jeremy Bentham is vice-president for global business environment at Shell and head of the Shell Scenarios team.