I was recently looking at the data for vehicle miles traveled (VMT) in the U.S. (From the BTS website: http://tinyurl.com/2dva4s)
From 1995 to 2005 VMT increased 2.12%/yr (ending up at 2.8 trillion miles). Extrapolate to 2050 and you get 7.1 trillion VMT/yr. If 60% of Americans drive PHEVs (as suggested by the report) at 0.3 pounds/mi (the low number in the graph), and 40% drive conventional vehicles at 1.0 pounds per mile, you get 0.6 pounds/mile. Thus annual vehicle GHG emissions would increase from 1.3 gigatonnes to 1.9 gigatonnes, despite the improvement from PHEVs. 60% PHEV-20s in 2050 is not good enough. Even 50% PHEV-20s in 2025 leaves the annual vehicle GHG emissions unchanged when we need a substantial reduction (25%) by then to meet the Hansen targets.

We need to run as fast as we can just to stay in the same place.
(Or we need to run as fast as we can just to keep up with our driving.)

Thanks for this post. I think there are a few factors that might mitigate against what you say. First, I’d be wary of projecting VMT out another four decades. Note that higher energy prices do seem to have slowed VMT growth recently — and there is obviously a limit to how many miles individuals can drive.

Second, if PHEVs are practical, I seriously doubt people will be driving PHEV-20s in 2050 — probably more like PHEV-60s (if not all electrics). Third, that chart does not include the possibility that cellulosic ethanol will be blended in with gasoline. If most vehicles are using E85 in 2050, and are PHEV-60s, (and gasoline prices are several dollars a gallon) then we can probably come close to the Hansen targets.

I agree with your points. It is just that the VMT trend was a bit scary, and it seemed worthy of a little bit of highlighting. I looked up the US population growth from 1995 to 2005, and it was 1.1%/yr, so that explains about half of the VMT increase. Projected population growth from 2005 to 2050 is 0.8%/yr, which might slow VMT a little. (The Census Bureau projects 420M in 2050. Gulp.) One hopes that oil prices will do a bit of slowing as well (let’s hope Peak Oil is soon).

Ignoring PHEVs for a moment, even if efficiency causes the US per capita electric use to fall 44% from 2003′s 11,997 kWh to California’s 6,732 kWh, the increase in population to 420M means total US electricity use only falls 19%. That means we need roughly another factor of eight reduction in g CO2/kWh in greenhouse gas intensity to meet the Hansen target.

Ignoring PHEVs for a moment, even if efficiency causes the US per capita electric use to fall 44% from 2003’s 11,997 kWh to California’s 6,732 kWh, the increase in population to 420M means total US electricity use only falls 19%. That means we need roughly another factor of eight reduction in g CO2/kWh in greenhouse gas intensity to meet the Hansen target.

I agree with your points. It is just that the VMT trend was a bit scary, and it seemed worthy of a little bit of highlighting. I looked up the US population growth from 1995 to 2005, and it was 1.1%/yr, so that explains about half of the VMT increase. Projected population growth from 2005 to 2050 is 0.8%/yr, which might slow VMT a little. (The Census Bureau projects 420M in 2050. Gulp.) One hopes that oil prices will do a bit of slowing as well (let’s hope Peak Oil is soon).

I was recently looking at the data for vehicle miles traveled (VMT) in the U.S. (From the BTS website: http://tinyurl.com/2dva4s)

From 1995 to 2005 VMT increased 2.12%/yr (ending up at 2.8 trillion miles). Extrapolate to 2050 and you get 7.1 trillion VMT/yr. If 60% of Americans drive PHEVs (as suggested by the report) at 0.3 pounds/mi (the low number in the graph), and 40% drive conventional vehicles at 1.0 pounds per mile, you get 0.6 pounds/mile. Thus annual vehicle GHG emissions would increase from 1.3 gigatonnes to 1.9 gigatonnes, despite the improvement from PHEVs. 60% PHEV-20s in 2050 is not good enough. Even 50% PHEV-20s in 2025 leaves the annual vehicle GHG emissions unchanged when we need a substantial reduction (25%) by then to meet the Hansen targets.

We need to run as fast as we can just to stay in the same place.

(Or we need to run as fast as we can just to keep up with our driving.)

Thanks for this post. I think there are a few factors that might mitigate against what you say. First, I’d be wary of projecting VMT out another four decades. Note that higher energy prices do seem to have slowed VMT growth recently — and there is obviously a limit to how many miles individuals can drive.

Second, if PHEVs are practical, I seriously doubt people will be driving PHEV-20s in 2050 — probably more like PHEV-60s (if not all electrics). Third, that chart does not include the possibility that cellulosic ethanol will be blended in with gasoline. If most vehicles are using E85 in 2050, and are PHEV-60s, (and gasoline prices are several dollars a gallon) then we can probably come close to the Hansen targets.

I agree with your points. It is just that the VMT trend was a bit scary, and it seemed worthy of a little bit of highlighting. I looked up the US population growth from 1995 to 2005, and it was 1.1%/yr, so that explains about half of the VMT increase. Projected population growth from 2005 to 2050 is 0.8%/yr, which might slow VMT a little. (The Census Bureau projects 420M in 2050. Gulp.) One hopes that oil prices will do a bit of slowing as well (let’s hope Peak Oil is soon).

Ignoring PHEVs for a moment, even if efficiency causes the US per capita electric use to fall 44% from 2003′s 11,997 kWh to California’s 6,732 kWh, the increase in population to 420M means total US electricity use only falls 19%. That means we need roughly another factor of eight reduction in g CO2/kWh in greenhouse gas intensity to meet the Hansen target.

Ignoring PHEVs for a moment, even if efficiency causes the US per capita electric use to fall 44% from 2003’s 11,997 kWh to California’s 6,732 kWh, the increase in population to 420M means total US electricity use only falls 19%. That means we need roughly another factor of eight reduction in g CO2/kWh in greenhouse gas intensity to meet the Hansen target.

I agree with your points. It is just that the VMT trend was a bit scary, and it seemed worthy of a little bit of highlighting. I looked up the US population growth from 1995 to 2005, and it was 1.1%/yr, so that explains about half of the VMT increase. Projected population growth from 2005 to 2050 is 0.8%/yr, which might slow VMT a little. (The Census Bureau projects 420M in 2050. Gulp.) One hopes that oil prices will do a bit of slowing as well (let’s hope Peak Oil is soon).

That means we need roughly another factor of eight reduction in g CO2/kWh in greenhouse gas intensity to meet the Hansen target.