"We cannot care for the planet without caring better for its people," Ms Short told a WWF conference on poverty and the environment. She welcomed the theme of the meeting.
Ms Short criticised Western hypocrisy on moves to protect the environment. "We are the major polluters of the planet - and now we are demanding that the developing world does not add to the pollution."
She noted that many in the South were "deeply suspicious that, having extracted all that we [in the developed North] needed to secure our economic development, we are trying to pull the ladder up after us."
She argued that environmental damage was inevitable in poorer countries: "It's poor people who often have no alternative but to over-exploit, and by so doing degrade the local eco-system on which they depend in order to survive."
The speech marked Ms Short's main policy statement on the environment, entitled: "Why the environment matters."
She has repeatedly tackled sensitive questions, including war and famine in Sudan, where she argued that aid to the hungry was "unnecessary" because it lessened the pressure for a ceasefire.
Ms Short argued that the Sudanese rebels' refusal to agree to a truce was an important reason why food was not getting through.
Her statements were enormously controversial, but many observers believe that they have been largely vindicated, and pressure for political change has had an important effect.
She referred to the figure that has become her crusading leitmotif - the "key goal" of reducing by half the number of people living in abject poverty by 2015, saying: "You may ask, `Why only half?' Because this is an affordable and achievable aim."
The development secretary argued against "doom and gloom and endless denunciations", and said that people should move "from passing the buck to finding the solutions". She argued: "It is when people know a solution that they demand action."
Ms Short used to be regularly described as "gaffe-prone". Even now, the theme occasionally returns. The Mirror newspaper published an article recently on "Clare's top 10 gaffes", which included her call in the 1980s for Page Three girls to be banned, and her statement in 1996 that the well-off should pay more tax.
Increasingly, however, her outspokenness has come to be seen as a strength. Where most politicians are perceived as spin-doctored, Ms Short is assumed to be speaking her mind, which, in her job, is a particular advantage.