Climate Impacts Day saw many brilliant campaigners across the globe join together to ‘connect the dots' between climate change and extreme weather events.

The message of the campaign, organised by the grassroots organisation 350.org, is bold and simple: 'Political action for a safe climate'.

In order to avoid the worst of the climate crisis, scientists tell us we must reduce the amount of CO₂ in the atmosphere from its current level of 392 parts per million ("ppm") to below 350ppm.

We know that 350 is where we need to be headed.

But both here in the UK and internationally, we are left with empty words and failed commitments on climate change.

So the Connect the Dots campaign couldn't be timelier.

In support of Climate Impacts Day, I joined 350.org activist Emma Biermann to put my 'dot' on the Houses of Parliament.  

Because despite repeatedly insisting that his Government is on track to be 'the greenest ever', Prime Minister David Cameron has shown little interest in tackling the climate crisis.

His disappointing speech at the recent high level Clean Energy Ministerial, attended by energy ministers from 23 different countries, showed that the PM just doesn't get it.

It was an ideal opportunity to show ambition for our trailblazing renewables sector and champion the potential for building a resilient economy through investment in tackling climate change, as well as addressing fuel poverty.

But Cameron's remarks were short on substance and commitment, revealing poor leadership, poor understanding of the risks posed by climate change and a poor grasp of the opportunities afforded by renewables and energy efficiency.

His level of inaction is reflected in international politics too, as we continue to wait for a global deal on climate change to follow the Kyoto Protocol which ends this year.

In an open letter on my Guardian environment blog, I call on Cameron to use the Queen's Speech tomorrow to send out a strong signal on climate change and commit to the 350ppm target.

The time for urgent action is now - we're already beginning to feel the disastrous impact of climate change in the melting of the glaciers, rising sea levels, acidic oceans and increasingly volatile weather events.

The Arctic is sending us perhaps the clearest message that climate change is occurring much more rapidly than scientists previously thought.

As James Hansen of NASA, the first scientist to warn about global warming more than two decades ago, wrote:

"If humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted, paleoclimate evidence and ongoing climate change suggest that CO₂ will need to be reduced from its current 385ppm to at most 350ppm."

***UPDATE*** You can read David Cameron's response to my letter here.