Caroline Lucas’s decision yesterday to step down at the next election came as a bit of a shock for the Green Party. After 13 years as an MP, 15 years as an MEP, 4 years as a County Councillor, and 11 years (on and off) as Party leader, she had quite simply come to personify the Green Party. Hers is pretty much the only name (outside the world of green politics) that anyone associated with the Party.

But the Green Party shouldn’t panic! Her inspirational leadership is one of the most important factors that have dramatically changed perceptions of the Party, encouraging far more people to get directly involved in one way or another than would otherwise have been the case, and helped build the kind of professional, electorally-savvy Party that was unthinkable even 15 years ago.

Which means the Party is in rude health. The local elections on May 4 were a triumph – gaining 240 seats and taking control of its first-ever Council in Mid-Suffolk; its co-Leaders (Adrian Ramsay and Carla Denyer) have grown in stature over the last few years, and will provide impressive leadership in the General Election; and many more voters now understand much more about what the Green Party stands for – and how critical its role has become.

But Green Party members are right to mark this as a special moment. The fact that Caroline is almost universally loved and respected across the Party (which can be horrendously fractious and factional!) is testament to the qualities she brought to all her different roles in the Party: total integrity; compassion and inclusivity; robustly saying it as she saw it; astonishing dedication – and a readiness always to do what she could for others; and as near to an “I am you and you are me” empathy as I’ve ever seen in a politician.

Those qualities did not go unrecognised by her fellow MPs – of all persuasions. They recognise what it is that makes for a great parliamentarian.

Listening to her interview with Nick Robinson on the Today programme yesterday, I was amused by the comparison made between Tony Benn (who stepped down as an MP to devote himself to his work on social justice campaigns) and Caroline, who is stepping down as an MP to be able to give more time to today’s Climate and Ecological emergencies in which we are already engulfed. That resonates so powerfully with me, having just stepped down from my work in Forum for the Future to do exactly the same.

Caroline has been kind enough in the past to remark that my book ‘Seeing Green’ played some part in her decision to join the Green Party back in 1986. However, I rather doubt that ‘Seeing Green’ had anything like as much impact on her as her career in the Green Party has had on me.

It’s all too easy to despair of our prospects of getting through these twin Emergencies. Frankly, those prospects go on getting worse, month by month. So I hang onto a few ‘reasons to be hopeful’ not quite like grim death, but like someone who knows that despair could be just one tweet or one link away, taking me to yet another scientific study pointing directly to civilisation-collapsing climate impacts.

Most of those ‘reasons to be hopeful’ are special people – dedicated campaigners, innovators, scientists, authors, a few business leaders, but no politicians – apart from Caroline. She has been an extraordinary inspiration to me for more than 20 years. The truth of it is that we cannot afford to lose faith in our political systems, let alone in democracy itself. In that respect, Caroline has given me so many reasons to ‘keep the faith’ – and for that I will be eternally grateful.