Former United Nations climate chief Christiana Figueres was a key architect of the landmark 2015 Paris Agreement, due to go into effect at the end of the year.

The Costa Rican diplomat spoke to AFP about her new book, "The Future We Choose", which lays out the best- and worst-case scenarios awaiting humanity as fossil fuel emissions continue to warm the Earth.

- 'Climate grief' -

Q. Why did you decide to write this book now?

FIGUERES: Three reasons. First, we wanted to reach beyond those who are dedicated to working on climate change. It's important to reach out to educated but less informed people, the critical mass that we need to reach in order to make the necessary changes.

The second is we really wanted to highlight that we have the most extraordinary responsibility/opportunity to wake up to the fact that we have one critical decade in which the human species is going to write the history of the planet for the next hundreds of years.

Thirdly, we wanted to create a sense of optimism and empowerment that we can do this. There's quite a bit of grief, despair and hopelessness around climate change. It's important to honour that grief but transform that into a can-do attitude.

Q. The book lays out best- and worst-case scenarios for the planet. Which do you think is the most likely?

FIGUERES: If we don't choose to act we are going to go in the direction of the first world that we describe -- a world that results from business as usual, that is a consequence of not choosing to do otherwise. It results in constraint and increasingly level of infrastructure disruption, human pain, biodiversity loss, economic fragility.

It is not a world we want to hand over to the next generation. It is however the world we are heading for unless we make the choice to do otherwise in these 10 years.

- Energy, transport, savings -

Q. Who is responsible for taking the choice to act?

Christiana Figueres was a key architect of the 2015 Paris climate accord / © AFP/File

FIGUERES: Everyone. We need systemic transformation that can only be designed by government policy and massive financial shifts and mass technology development, mainly from the private sector.

But equally important is individuals waking up to the opportunity that is staring us in the face. Consumer demand sends very strong signals to business.

Q. What are three things we as citizens can do to help?

FIGUERES: If we live or work in homes or offices that are energy inefficient the very first thing we should do is get an audit and figure out where we are wasting energy. If we don't do that we are hurting the planet and our wallets.

Another place we can change is transport. The more we use ourselves to transport ourselves the better it is for our planet and our health.

Finally, not everyone is in the happy position of having savings. But those who are should really look at where those savings are. Most financial institutions have realised that a sizeable presence of high-carbon assets is very risky and they are beginning to shift. We should be asking whoever is managing our assets if they are in the right place. Are they safe?

- Big economies must step up -

Q. Five years since the Paris deal, emissions are still rising. Are you still confident the agreement is fit for purpose?

FIGUERES: There is very little left to negotiate at COP26 (climate negotiations in Glasgow in November). This is more about the five-year cycle included in the Paris agreement where countries make a decision on shifting capital, increasing technology and progressing policy. Those three things should allow them to increase their ambition.

There are only a few countries that have registered their new emissions reductions plans, we know that there are around 80 countries that will be doing so as we get closer to COP26. That's not necessarily good news because many of those are small economies. What we really need is the large economies to be doing more.

Q. Do you see any possibility of a successful outcome at COP26?

FIGUERES: French diplomacy was absolutely critical to the Paris agreement jumping over the line. I am confident that the UK realises that this is the most important COP since Paris, that we have to send a signal that it is on track, and that the UK will deploy its very effective diplomatic capacity throughout the world to get countries ready to come to Glasgow with new ambition.