Failure to act now will make the problem more difficult to solve in future

Small annual increases in population - what's the problem? Mathematically, the problem is simply that of compound growth. A population growing at just 1% a year (UK population is growing at 0.7% a year) will double in 70 years; and a population growing at 2% a year will double every 35 years. So what looks like negligible growth in the short-term becomes catastrophcially unsustainable growth in the long term. The greater the overshoot, the steeper the reversal would need to be.

Ecological footprinting calculations indicate that a sustainable UK population size, on the basis of equitable worldwide allocations of carbon dioxide emissions and biological resources, may be lower than 20 million. Just as delaying action on greenhouse gas emissions makes it more difficult to halt dangerous climate change, delaying action on population growth makes future population growth reversal more painful. UK population reached an estimated 60.9 million in mid-2007 and is now growing by more than 350,000 a year. Rapid population decline, however, can result in population ageing at a speed which would be economically unsustainable. OPT's suggested target - to achieve a gradual decrease from 60.5 million to 53 million by 2050 - a reduction roughly equivalent to the population of London - would have involved an annual decrease of 0.3% a year from 2006 to 2050. An annual decrease of 0.25% would not achieve 53 million until 2058. Had a policy been set in motion in 2000, the annual reduction need only have been 0.25% to reach 53 million in 2042 and 51.8 million in 2050. But a population stabilisation policy put into effect in 2007 (average family size at replacement rate and zero net migration), even assuming no further lengthening in life expectancy, would reach peak numbers at just over 63 million in 2026-27, and decrease only to 62.2 million by 2050. See the ONS 2006-based Stationary Projection published in 2007.

Offical UK population projections

Official population projections are published by the Government Actuary's Department, now part of the Office for National Statistics, and they have underestimated actual growth rates for many years. The latest projections (2006-based) were published in October 2007, after fertility, migration and life expectancy assumptions had all been upwardly revised. These show what can be expected if the government pursues its implicit pro-population growth policy and if other political parties fail to offer people in the UK an environmentally sustainable alternative. The Variant Projections show variations in one component of change, with the other components remaining as in the Principal Projection. A full report on the 2006-based National Population Projections was published in June 2008.

See OPT Press Release of 8 February 2005.

Population Policy Projection 02/A/00 (see below) had been published by OPT on 29 September 2002, using a constant fertility/zero effect migration variant of GAD's 2000-based population projections. If implemented in 2000, it would have allowed UK population to reduce gradually (by about 0.25% a year) to 53 million by 2050.

At 2050, it would have been possible to continue to allow numbers to decline to a possible long-term sustainable level of 30 million by 2121, or to remain stable if very high-risk environmental impacts have been averted. A second projection (B) was also commissioned, to demonstrate the difficulties (such as faster population ageing) of achieving a more rapid reduction. These projections were commissioned from the Government Actuary's Department but are not official government projections. However, the 2003-based 'Natural Change Only' population projection published by GAD in 2004 was broadly similar. To view these, you will need a free Excel Viewer.

OPT POPULATION POLICY: PROJECTION 02/A/00. This assumed that the current TFR (total fertility rate) would continue at its 2001 sub-replacement level of 1.64 births per woman, that life expectancy would remain at the level used for GAD's Principal [Population] Projection 2000 , and that the effect of migration is zero (ZNF=zero net effect, not to be confused with zero), implying numerically balanced levels of emigration and immigration. A population of 52.5 million would have been achieved in 2050 and a target of 30 million, if necessary, would have been achieved by the year 2121.

OPT POPULATION PROJECTION 02/B/00 For demonstration purposes only. This used the above assumptions except for the total fertility rate, which was reduced to 1.4. A population of 30 million would have been achieved by the year 2087 but the mean age of the population would have risen by about 10 years by 2100.

Moving the goalposts

Rapid growth in population over the five years since the first of these policy projections were commissioned from the Government Actuary's Department (GAD) will make population stabilisation and decrease even harder to achieve.

In 2004 GAD published its 2003-based projections showing UK population in 2050 . The Principal projection forecast 66.78m in 2050, the High Migration variant 70.7m, the High Fertility variant 71.18m, and the Natural Change only variant 56.98m.

In 2005 the ONS (formerly GAD) published its 2004-based projections showing UK population climbing faster, with the Principal projection indicating 69.2m in 2050, the High Migration variant 73m, the High Fertility variant 74m, and the Natural Change only variant 57.7m. No projections were published in 2006.

In 2007 the ONS published its 2006-based projections showing UK population faster yet again. The Principal projection indicates 77m in 2050.