A long time ago, people used to live in harmony with nature. But as time passed, we humans started using more and more resources, cutting down forests, polluting the air and water, and doing a lot of other things that were not very nice to the planet. All of these things together are called climate change, and it makes the planet hotter and harder to live on.
London Climate Change Agency is a group of people who work together to figure out what we can do to stop climate change from getting worse. They try to find ways to make sure London (which is a big city in England with lots of people and buildings) doesn't make the planet even hotter.
They also help people understand what climate change is, and why it brings problems like heatwaves, floods, droughts, and storms. They figure out ways to reduce carbon emissions (which are like bad smells that come out of cars, factories, and other things). They help people change their homes and buildings to be more energy-efficient (which is like making sure that they use less energy, and therefore produce less power and emissions).
Basically, the London Climate Change Agency is like a big team of superheroes who are trying to save the planet by making sure that everyone tries to protect it.