Só até certo ponto mais CO2 pode funcionar como "fertilizante".
Na realidade, a partir de uma determinada temperatura, a fotossíntese pode sofrer um colapso:
«Higher temperatures can reduce or even halt photosynthesis,
prevent pollination, and lead to crop dehydration. Although the
elevated concentrations of atmospheric CO2 that raise temperature
can also raise crop yields, the detrimental effect of higher
temperatures on yields overrides the CO2 fertilization effect for
the major crops.
In a study of local ecosystem sustainability, Mohan Wali and
his colleagues at Ohio State University noted that as temperature
rises, photosynthetic activity in plants increases until the
temperature reaches 20 degrees Celsius (68 degrees Fahrenheit).
The rate of photosynthesis then plateaus until the temperature
hits 35 degrees Celsius (95 degrees Fahrenheit), whereupon it
begins to decline, until at 40 degrees Celsius (104 degrees
Fahrenheit), photosynthesis ceases entirely.17»
in PLAN B 3.0 Mobilizing to Save Civilization Lester Brown Cap. 3
Rising Temperatures and
Rising Seas
http://www.earth-policy.org/Books/PB3/pb3ch3.pdf
Em relação ao vídeo do Attenborough, e então?