In a Business 'As usual senario,' global CO2 emissions reach 64 GtCO2 y -1 by 2050. Convert this figure to GtC y-1, and calculate the percentage increase from the level of global CO2 emissions in 2004, estimated as 8.8 GtC y-1.

To convert CO2 emissions from gigatonnes of carbon dioxide (GtCO2) to gigatonnes of carbon (GtC), you need to take into account the carbon content in CO2, which is approximately 27.3% by weight.

Here's how you can calculate the conversion:

1. Start with the value of global CO2 emissions in gigatonnes (GtCO2): 64 GtCO2/y.
2. Multiply this value by the carbon content percentage (27.3%) to get the emissions in gigatonnes of carbon (GtC):
64 GtCO2/y * 0.273 = 17.47 GtC/y (rounded to two decimal places).

So, 64 GtCO2/y is equivalent to 17.47 GtC/y.

To calculate the percentage increase from the level of global CO2 emissions in 2004 (8.8 GtC/y) to the projected level in 2050 (17.47 GtC/y), you can use the following formula:

Percentage Increase = ((New Value - Old Value) / Old Value) * 100

Substituting the values:

Percentage Increase = ((17.47 GtC/y - 8.8 GtC/y) / 8.8 GtC/y) * 100
Percentage Increase = (8.67 GtC/y / 8.8 GtC/y) * 100
Percentage Increase ≈ 98.5%

Therefore, the percentage increase from the level of global CO2 emissions in 2004 (8.8 GtC/y) to the projected level in 2050 (17.47 GtC/y) is approximately 98.5%.