Most of us live most of our lives in one or more parallel universes. The first universe is the world of the immediacy of each of our everyday lives - getting to work, paying the bills, concerns about rents and mortgages, families and our own immediate lives and personal futures.
The second parallel universe which we occupy when we have time is that of the wider world: Of today's headlines - killings in Syria; insurgency in Iraq; The Arab Spring.
The third parallel universe in which we occupy in every sense is that of the natural environment. However, all too often we don't have time to concentrate or consider what is happening in our natural environment until we can get through the looking glasses and wardrobes of the various earlier concerns and preoccupations of the various earlier parallel universes.
A quarter of a century ago, the Brundtland Report introduced the idea of sustainable development to the international community arguing that it could be achieved by a policy framework embracing economic growth, social equality and environmental sustainability.
Sustainable development was defined by Our Common Future, the landmark report of the World Commission on Environment and Development published in 1987, as development that "meets the needs of the present without compromising the ability of future generations to meet their own needs." In other words, we should not steal from our grandchildren.
In this sense, sustainable development is not a destination but should be a dynamic process of adaptation, learning and action. It is about seeing the whole picture, such as the critical connections between food, water, land and energy. Sustainable development is about ensuring that our actions today are consistent with where we want to go tomorrow.
So it is clearly sensible to ask how much has really changed since the Brundtland Report or since The Earth Summit, the United Nations Conference on Environment and Development, which was held in Rio de Janeiro in 1992, or indeed since the reaffirmation of the Rio principles at the Johannesburg Summit in 2002.
The fact is that progress has been made, but a more disturbing fact is that the world is not on the path of sustainable development. And the simple truth about unsustainable development is that it is, by definition, unsustainable. There are a number of things that the world needs to do urgently even before 2020.
In 2000, the world made a promise to halve the number of people living in extreme poverty by 2015 compared with 1990. Today, the world is on track to meet that target - however it should be noted that more than a quarter of the world's population - some 27% - still live in absolute poverty. So although global economic growth is up 75% since 1992, inequalities are still high.
The per capita income difference between rich and poor countries has grown continuously. The gap between rich and poor has widened in many developed countries in the past twenty years and the average income of the richest 10% of the population is now about nine times that of the poorest 10%.
The world now has a population of some seven billion people, and indeed as the world's population has grown to its current level of seven billion, food production has kept pace. Today enough food is still produced to feed all of us comfortably. However, access to food is another matter.
Hunger has risen seriously in recent years and the number of undernourished people in developing countries increased by about 20 million in recent years. There are serious issues about prices and inputs, such as fertilisers, water availability and competition for land. Mahmat Gandhi once observed that, "earth provides enough to satisfy every man's need but not every man's greed".
With the majority of the world's people living in coastal areas, oceans are crucial for humanity's future - whether through direct economic activities or because of the environmental services they provide. However, overfishing has led to 85% of all fish stocks now being classified as over-exploited, depleted or fully exploited.
As for climate change, there has been a 38% increase in annual global carbon dioxide emissions between 1990 and 2009. Despite the adoption of the UN's Framework Convention on Climate Change and the Kyoto Protocol, annual global carbon dioxide emissions from fuel combustion grew by about 38% between 1990 and 2009 with the rate of growth faster after 2000 than in the 1990s. Even with serious action to reduce emissions, the world could still face challenges to limit global temperature increases to 2°C since pre-industrial times.
Among its expected impacts are reductions in crop yields, particularly at low latitudes where most developing countries are, change precipitation patterns and reduce water availability, increase land degradation and desertification, negative impacts on human health, sea level rise likely to pose a threat to some smaller islands, developing states and communities and countries with large coastal areas and new risk from extreme weather. These risks are particularly severe for the world's poorest.
The problem is that the concept of sustainable development has not yet been incorporated into the mainstream national and international economic policy debate.
I think a large number of economists still regard sustainable development as extraneous to their core responsibilities for macro-economic management and, of course, it is challenging having on the one hand to increase growth in economic activity so as to help take millions of people out of poverty, whilst at the same time trying to ensure that such growth can be sustainable.
But all too often we have treated areas such as food, water and energy as being separate issues whereas all three need to be fully integrated and not treated separately if we are to deal with the potential crisis in global food security. We need to spend much more time considering planet "pantry" boundaries, "tipping points" and "environmental thresholds".
Few goods and services sold today bear the full environmental and social costs of production. We only measure development as growth in gross domestic product but perhaps we should develop a new sustainable development index or set of indicators.
Sustainable development is about seeing the whole picture, such as the critical links between food, water, land and energy. I think one of the reasons why we have failed to make greater progress on the sustainable development agenda is that for many decision-takers, there is a feeling that it can be business as usual for just a bit longer.
I think we have to be careful if we think that we can simply shut off responsibility for our actions today to our children or grandchildren. There is evidence to suggest that climate change could well be abrupt as well as linear. Indeed, it has been claimed that the impact of climate change is likely to be greater on developed societies, such as Europe and the United States, because of our lack of resilience.
I think it would be a brave person who believed that intense climate change events won't, for example, be without risk of immediate security implications. There are pollutants other than CO2 that contribute to global warming, namely Black Carbon and Ground Level Ozone which are not part of the negotiations on greenhouse gases. HFCs could be controlled efficiently under the Montreal Protocol which has already successfully phased out nearly a hundred similar chemicals.
What the United Nations Environment Programme has recently shown is that an approach concentrating on these short term climate drivers, which account for 40-45% of global warming could buy humanity several decades of breathing space by cutting the rate of climate change nearly in half through 2040 or beyond.
But I think partially because there isn't the sense of urgency and partially because the science behind this isn't perhaps widely enough understood, little action in this regard is being taken.